Goat Simulator
Garry's Mod
[DOUBLEPOST=1432153790,1432153715][/DOUBLEPOST]Geometry Dash
Orange Box // All the Half Life 2's
Hitman Absolution
Left 4 Dead 2
Rust
Train Simulator 2015
Software Inc, Besiege, Cities: Skylines, Rust, Killing Floor 2 and Reign of Kings.
All of these fit in your price range, and all of them are pretty amusing.
Depends on the games you like? I strongly recommend Company of heroes Tales of Valor (TOV) and maybe even Company of heroes two. Both great ww2 strategy games, great fun.
The Elder Scrolls V: Skyrim is still a pretty good game for it's price (6€) and if you buy it on pc the modding abilities are endless. You can also get gun mods so it'll be kind of an fps