Used Price Shakedown

I was looking at Destructiod's Buy and sell games powered by Glyde, and I occurred to me that I could buy a lot more games for my dollar. I prefer brick and mortar stores, but we have all known for a long time that GameStop tries to squeeze every last ounce of profit from their used games. Here's a quick Shakedown for a randomly selected group of games:


GameStop:
Black Ops: 54.99
Portal 2: 34.99 (sale price)
Crysis 2: 34.99 (sale price)
Total: $124.97 or 89.98 B2G1 (with edge card, $112.47 or $80.98)

That's actually a little better than GameStop's average, but only because two of the randomly selected games were on sale. $90 looks like a good deal until you check at Destructiod and Amazon:
Destructoid (with Glyde):
Black ops: $28.25
Crysis 2: $26.00
Portal 2: 
shipping: $4 - $12
Total: $87 - $95


Amazon:
Black Ops: from $29.99
Crysis 2: from $29.95
Portal 2: from $32.00
Total: $91.94 (before shipping)

So, Destructoid is very close to Amazon in price, but is like a B2G1 sale at Gamestop. I have considered trying Gamefly, but I like building my collection. I like that Destructoid gets a share of the profits, because I feel that they are what Kotaku used to be.