games that were worth more money than you paid for

[Man 2]

Civilization IV. Bought it used for $3.99, haven't ever regretted it.

[Ad Bot]

[Cargøn]

Bastion
Hotline Miami

[Zalot]

minecraft
i got it for like 5$ back when it first released
it was super cheap

Warband
got it for 20$ and put over 200 hours into it

[Tomcat]

Civ4 and Killing Floor

[uno_da_cat]

Binding of Isaac, which seems to be a group consensus for most. $2.50, 40 hours.
Dead Pixels, a $2.50 game I got for free and ended up with 30+ hours.
Garrysmod, $10, almost 1000 hours.