5.3 GH/s @ $149 = $28/ghps
It actually costs $274.
They are comparing the historic prices of BFL and Avalon. If you're going to use the current price for the BFL unit then you must do the same for the Avalon, which is more than $10000 at current prices.
BFL has no prices for products. One must first
have a product before it can be assigned a price.
So far, BFL is selling zero-coupon convertible debt with no maturity date.
At some point in the future, the debt might be convertible into a black box assembled by amateurs that might mine bitcoins for some indeterminate period of time.