Harris was THE bipod for quite a while, and they still are pretty popular. The base models are around $100 though... and lack canting ability.
Alot of guys like the Atlas bipod... but they are quite expensive. They have interchangeable feet though. http://www.accu-shot.com/Atlas_Bipods.php
These usually mount on a rail that's fitted to the stock.
The versa-pods have a mount adapter for a sling swivel, or a rod that you can sink into the front of the stock. They also have interchangeable feet. http://www.midwayusa.com/product/787833 ... feet-black
If you want to stay under $50, then just about any harris knockoff will work. Caldwell, UTG, that NcStar, Blackhawk, and a myriad of others... are all knockoffs, and the difference in price is reflected in better materials.
For cheaper bipods, I've got one caldwell... and two Blackhawk. The nice thing about Blackhawks is that Wal-mart carries them. They also have a cant ability, and the prone/bench model is around $45 I believe.
Also, just about all the harris knock-offs mount to a sling swivel.
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