I truly like Basic Fantasy. While not quite a clone, i can run adventures from Basic D&D to 3x to the various clones and the editions in between with minor conversions (if any) on the fly.
The price is certainly right, as the PDF for the core game and all the adventures and supplements are free and the print versions are at cost.
The 3rd edition of the Basic Fantasy rules just released as well as the Basic Fantasy Field Guide, which is a monster book with over 180 creatures for your BFRPG game or any other OSR or old school RPG.
Basic Fantasy 3e is currently $4.18 in print at Amazon and the Basic Fantasy Field Guide is currently $3.61. Amazon prices can swing a bit in either direction. Both ship Prime if you have Prime. They should also be available on Lulu.