Counter-Strike: Source, Day of Defeat: Source, and Half-Life 2: Deathmatch is $30
Half-Life 2 is $20
Half-Life: Source, Half-Life Deathmatch: Source is $10
CS 1.6 is $10
Team Fortress Classic, Opposing Force, Half-Life, Half-Life: Blue Shift is $15
So in total the account is worth about $85 just for the games on it.
Anything less then about $45 and I would be selling the account for half what its worth.