http://www.newegg.com/Product/Product.aspx?Item=N82E16813157304 would be the best for sub 100. It would help us a lot to know what your using with the processor and the budget for the motherboard though.
your not going to get anything for $50 new. I got a h61de/s3 off ebay for 35 shipped and as bottom as it is, it is like $70 http://www.newegg.com/Product/Product.aspx?Item=N82E16813157254.
You really need a bigger motherboard budget.
ok. Chipsets for one. They are the brains of the motherboard and control everything. Z77 is the best, followed by Z68 and P67.
more expensive boards have higher expandability and just general higher quality.
also your overclocking and BIOS options of the cheaper ones are probably going to be limited.