It's all about reducing the power bill for me.
Then you should consider modern FPGAs like Icarus and X6500. Way more power efficient. BFL Singles will become unprofitable long before other FPGAs.
I'd need 3 or 4 of those to match the hashrate, at 3 or 4 times the price, so no
3 or 4?
Sure BFL is lower MH/$ but you might have forgotten to carry a 1 or something.