Hello Bodgan,
what router to buy depends on what the ISPs are going to send to your router.
if you receive only default routes and you have your own ip address block you can use a C3825 or c2851.
If you want to receive two full tables (not required and not recommended in your case) you should go to a C7206VXR with NPE G2
if you have already a powerful multilayer switch on the site if all the links are lan links you could consider to have the eBGP sessions over it/them.
This can be cost effective.
Hope to help
Giuseppe