friedcat seem to be the cheapest currently. But requires some DIY from what i can see.
Alternative if you want a hitnrun go with the S3.
However.. ROI is unlikely at the current btc price, so you'll have to hope for a rise in value.
ASICminers stuff doesn't use "normal" mining software,I'm not too keen on them for that reason,it's a bit involved in getting it to mine & only at certain pools
S3's seem the only decent choice ATM......easy to setup,decent power consumption,ok price.........
With ya on the ROI thing mazedk,just hold your mined BTC
Personally hoping BTC hits $100 for 6 months..........weed out the farms........maybe