A quick eBay search turned up an AFV Club M10 for $18 and an Academy M10 for $15.
AFV Cub's kit has some annoying gimmicks like a spring loaded recoil system and vinyl rubber inserts for the suspension bogies. Academy's kit has better interior details within the hull, but experts say the AFV turret is more accurate. Purists recommend the AFV turret on the Academy hull; something I'd never bother to do! I have both kits and would recommend either, but tell you to get which ever kit you find cheaper.
Having said all that, there's probably more aftermarket items designed for the more common Academy kit than for the less common AFV Club kit. That's something to keep in mind. The Academy kit has been released in at least three versions as has the AFV kit.