USRP alternatives for CR / DSA application

Hello all,

Currently I am in the opening stages of a senior design project for my
EE
degree. My end of the project will be to implement a CR / DSA radio
using
the GNU platform but not necessarily using the USRP as the platform of
choice. Looking for alternatives to the USRP, I was wondering if there
was
some sort of consolidated list of single board computers / processors
known
to be compatible with GNU. If such a list does not exist, any
suggestions
would be much appreciated. The only parameters that are necessary to
follow
for the design is that the single board computer must have GB 10
Ethernet
and the price is capped to $500.

Thank you well in advance,

-Tim