Nah, the Spiral Knights one isn't so bad. You basically just need enough money to buy the item. Around 1000 is enough since that's what the "buy it now" prices at the auction house were at when I got it.
I think if you do the stuff required to get the TF2 hat, you should have around enough money to get the bomb for the achievement.
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Ginhyun
'Cause tramps like us, baby we were born to run