Basic Fantasy just turned 10 years old a few days ago. It's an amazing RPG that emulates classic B/X D&D but not strictly. For example, it uses ascending AC, which is really easy to convert from D&D modules: just subtract the D&D AC from 20 and that's the new Basic Fantasy AC. Also, it divides race from class so now you can be a dwarf thief or a halfling fighter if you like. There are a few other differences but pretty much everything else is classic B/X D&D and I love the simplicity. I love the flexibility and the race divided from class adds to the flexibility.
I've run D&D modules and AD&D modules with Basic Fantasy just fine. There also a bunch of free modules and supplements on the Basic Fantasy site. Everything is free and open source and everyone is welcome to contribute. In fact, many of the existing retroclones are based on Basic Fantasy. Take a look at their OGL section and look for the copyrights. That's the beauty of Basic Fantasy - it's a perfect base for you to build the RPG that you want on.
Also, because it is all non-profit, you can get the books at cost through Amazon or Lulu or RPG Now. The rulebook is only a bit over $4 for a softcover. The downside to doing everything for free is that all art is donated and it doesn't have the incredible art you'd get if you buy the latest edition of D&D. The art is good though and some of it is amazing. Please let me know what you think of Basic Fantasy!