Check out mg 995 from ebay. $14 a pair with solid metal gears and double ball bearings. they are not as presice as the hitecs, but they are pretty fast and strong(15kg/cm @ 6v). Have used them for lots of apps and you wont fint stronger standard size servos at that price.
NOTE: I've gotten some thats not 100%. where the gear is a bit malfuntioning and stuff. But you get 4 of these for the price of one hitec which is half the torque.