Sorry. No free/cheap way to do it. I have done (I think) over a thousand scores for BHS, rewriting them to meet current BHS notation standards.

If you have a Windows computer, you can still purchase PrintMusic 2014. That will let you play back, depending on how the .mus is done. However, that will lack a number of features necessary for quality PDF charts.

Feel free to drop me an email if you want more details. My address is in my signature.

I'd suggest downloading the demo, and then spending 30 days batch converting all documents to both PDF and MusicXML...!

Good idea, Ben!

Mac or PC ? (Please add the infos to your Signature/Profile). On PC, Notepad (free) and Printmusic (not very expensive) are available on the MakeMusic website.

https://www.finalemusic.com/products/ 

NotePad won’t do what he needs, for sure. PrintMusic will, except for some details in printing the score. I used to use PM for barbershop charts and playback, until I really needed the printed scores to be correctly done. That took an upgrade to Finale.

Possible flag on the play! More than one app generated .mus fies. Yes, really and those generated by one app cannot be read by another.

The two most popular were Finale (through 2011) and MusicTime/MusicTime Deluxe. So do download the Finale demo and see if they will open at all. If they open and look wrong, that still tells you they were Finale files and that can be dealt with.

If they will not open at all, head over to passportmusic.com and download the demo for MusicTime Deluxe and see if that works. MTD is 32 bit only and works in Windows and MacOS 10.14 Mojave and earlier. I don’t know that you can print or save to pdf while in demo mode—I’ve not owned it since version 2 when you couldn’t. MTD is less expensive, however, and you may have to purchase to print. If your files open and print in MTD, the only way to convert them into a version that can be read by other notation apps is to print to PDF so that a scanner app can read them. MTD/Encore’s MusicXML 1.1 does not export lyrics — not good with barbershop scores.

I’m remembering that there were other apps that used the .mus extension and if your files were generated by any of them… well, hope that Finale or MTD can open them.

This was nagging me so I did a little more digging. Here's more info on the .mus file type. 

https://filext.com/file-extension/MUS 

This site has a great feature, a drag and drop window that can try to analyze a .mus file. It correctly identified some very old Finale files going back to 1994. Unfortunately, it could not identify any of my old MTD 2 files as other than "generic binary".

I know that Harmony Assistant still exists though they changed to a different file type in 2013—it's also cheap and there's a demo. Although HA fanboys tout its ability to open other file types, I've never experienced anything better than dreadful results. I've no idea what to do with a SCORE .mus file anymore.

Highly unlikely to be one of these one of these others: .mus - Doom music file, .mus - Infinity game engine music control data, .mus - Musifile MPEG Layer II audio stream, .mus - Sony PlayStation 2 music data, .mus - Minecraft music, .mus - Need for Speed: Most Wanted music

For kicks, I did try to open an old MTD in Finale and received the following as expected:

Finale cannot open the selected filetype. Please select another file.

Good luck!

How many songs can you access (you said “Hundreds of them”)? Let’s say, 200. If you bought Finale for $600, that’s $3 each to get those songs divided into part-predominate tracks, and a clean, printed score. Or, you could buy PrintMusic for $119, and upgrade to Finale for $149 more. So now, your cost is $278, or $1.39 per song.

If you were to ask me to do it, I would probably charge $20-25 per song. So a buck thirty nine a pop sounds pretty reasonable. How many people in your chorus? Would they split the cost to subsidize the purchase? Can you qualify for a student or theological discount?

Or, send me a sample score, for one freebie. My email is encoded in my signature.

" I'd suggest downloading the demo, and then spending 30 days batch converting all documents to both PDF and MusicXML...!"

Does Finale 27 demo export xml?  Does it print PDF? I was not aware that it did either.

>Does Finale 27 demo export xml?  Does it print PDF? I was not aware that it did either.<

Yes to both for the 30 day evaluation period and then it won't. The 30 demo is fully functional with only one limitation: You do not get the Garritan Instruments for Finale (GIFF) until after purchase. Of course, if upgrading, you already have GIFF from the previous version.

Once purchased, you get a new download link that includes the purchased version plus separate downloads for the Aria Player and GIFF.

Back OT. This will not work for the OP if those .mus files were not created in Finale to begin with. I've already made other suggestions if that turns out to be the case.

I thought the demo didn't save anything or print anything but I don't ever remember d/l the demo so I didn't really know.

The demo doesn't save or print (nor export, probably) after the 30 days of full function have expired.

> thought the demo didn't save anything or print anything but I don't ever remember d/l the demo so I didn't really know.<

There was no demo or download before 2012 and I don't remember what it could or couldn't do.

>The demo doesn't save or print (nor export, probably) after the 30 days of full function have expired.<

We've seen the "I paid — why can't I print (or save or…) anymore?" posts here. The answer, of course is that the user is still running the demo and needs to download the purchased version from their User account and register it properly.

For myself, I hate demos. I'd rather pay the upgrade/crossgrade etc. than limit myself to 30 days to figure out an app well enough to know if it's going to work out for me. I only do this with pro apps that have a learning curve (Dorico) or ones I need for a client (Notion 6, Logic Pro), however. If I think I'll know after a few minutes that an app will or won't have basic functionality I can use, then I'll download a demo.

Perhaps not the wisest course or best practice but I have a habit of upgrading all of my software when they become available.

That's why I am unfamiliar with the functionality of the Finale demo. I don't d/l it and try it first. I confess, I have d/l the Sibelius demo several times as they upgrade, so far it is a no-go!

In Finale's case I always keep the previous version fully functioning before I uninstall it. Some versions have been better than others for sure but all of them have done what I wanted or needed to way or the other. My history goes back to Finale 3, which I believe was in the late 1980's or early 90's, and then Finale 97 as they switched to years.  I still have the boxed sets somewhere around here.