Most fun you had for the lowest amount of money ?

Dota 2!

super hexagon

Recently, that is, on Steam.

Killing Floor-free

Ultima Online, don't know how many hours I spent on that game, but it's a lot

Terraria probably. And I didn't even buy it on sale.

Compass

team fortress 2

MTG: Duels of the Planeswalkers 2013. This was only five bucks when I bought it, and wow is it fun.
I stopped playing because apparently switching to Verizon FiOS breaks the multiplayer. :C

Binding of Isaac.

Dota 2

I can't choose between HoMM III and Morrowind. For 3 cd's for each title(counting dlc's) i paid at that time around 300-400 roubles(it's 10-13$), and I still play both of these games.

Probably The Binding of Isaac, or Portal 2 maybe

Playtime with myself is years, and it is free. Pretty good deal I would say.

DotA for about 20€ because DotA 1 and 2 and WC3 TFT costed me 20€ :)

DOTA2 to be honest, even if I've stopped playing for several reasons I paid a extremely low amount of meony per hour (I did pay for it, and it was not a very small amount, but I got it when it was decently new)

TF2 Probably

Canaan Online, some naff browser MMORPG.

Hmmmmm, Team Fortress 2 I guess.

binding of isaac.

Fallout 3 with all dlc's for £10 over 350 hours of fun

Diablo II + Lord of Destruction Expansion == fourteen years of entertainment for only $60.

Neverwinter Nights also continues to keep me entertained after all these years, but I paid about $200 for the game and expansions.

Basketball. I played it at my house with my friends. For free.

Didn't even pay for electricity

Where did you buy that?

I think it's Binding of Isaac. $1 for 113 hours.