I don't know about any Cheap $40 Graphics card which enables you to play Gmod and Team fortress 2 at High Settings and at least 30 Fps.
A list of a few graphics card, I've searched for you:
Radeon HD 4350 is priced at just $39 for a 256-Mbyte configuration, while the Radeon HD 4550 is priced at about $55 for a 512-Mbyte configuration-
http://www.extremetech.com/article2/0,2845,2331409,00.aspA $15 extra should not be such a challenge, I hope.