Well italian firearms tend to be on the cheaper side, same with the russian arms. Though both of them require you to start reloading if you want to keep costs down.
Enfields would be your best bet. 300-400$ range and ammo can be found everywere.
French firearms and japanese tend to be less common and high priced. Reloading seems to be your only option.
American firearms command a premium , M1 , garrand, and springfield.
Germany mausers are in the same price range as the american rifle (poor condition starting at 500 up to 1000 for a nice unit), the semi autos are rare and pricey.
Pistol wisfor those on a budget you have webley/enfield , tt-33, p-38, all of which can be found under 300
Keep in mind you excluding some great shooting firearms like all of the swede firearms (both bolt and semi) , and the whole swiss straight pull line up. Don't limit yourseld in that area as these firearms are noted for build and accuracy.