Have you considered that, perhaps, the fact that you use a template file for this project that is proprietary to an obscure, rather expensive software package may put off some folks who might otherwise consider joining this project? It may or may not be the Royals Royce of hex editors, but $50 seems a bit high for a single home license.
At least the use of proprietary Micro$oft software is understandable, because it's so popular and common anyway that one probably already owns it and there'd be obstacles to using an alternative (assuming it exists). But there are numerous free and relatively inexpensive hex editors available with respectable features, if one searches enough. It's just that commercial software is advertised a lot more and non-free hex editors are easier to find.
For example:
Frhed - Free Hex Editor - Free, open-source software with many advanced features
Free Hex Editor Neo - Free, lots of features
HexEdit - Free hex editor with numerous features, including a powerful expression calculator
Advanced Hex Editor (A.X.E.) 3.4Shareware - Lots and lots of advanced features.
Cheap OEM Software > Advanced Hex Editor 3.4 - Same as above, but can purchase at a
much cheaper price
Of the ones mentioned above, I've tried them all with the exception of Free Hex Editor Neo. And I've found each one to be capable, depending on one's needs and usage. Usually, however, I use either Frhed or AXE.
Edit: I found one more, and it looks pretty nice:
WinHex - Computer Forensics & Data Recovery Software, Hex Editor & Disk Editor. The variety of features seems downright enormous. Website states, "Try before you buy, as long as you need, for free." (Back in 2002, a much older version of WinHex placed first on
Harrys Windows Hex Editor Review in terms of features.)
BTW, a lot of software available for "free download" nowadays have either very crippled features or are simply demoware that stops working after a trial period. But sometimes one can find
earlier versions of the same program (particularly Shareware) that are either completely free or do not have such limited functionality.
Oh, and the following Wikipedia comparison of various hex editing software seems very thorough. I never knew there were so many different hex editors under so many difference licenses under different platforms!
Comparison of hex editors