Of course, that's the cost. But how much do you have to spend in bitcoins to drive the price up that much?
e.g. buying $800K worth of bitcoin in 15 minutes, so that you can increase the price of BTC and then buy $5M worth of goods NewEgg - would $800K in fifteen minutes press newegg's btc-denominated price well below wholesale on those same electronic goods? (including to cover what you overpaid for the btc to execute your position.)
You might temporarily drive up the exchange price sharply, but at the cost of buy a ton of BTC at an inflated price.