Get a BFL Little Single for 14-15BTC off forums here or bitmit. Better than Blades @ 24BTC for same production.
Actually, the cheapest BFL Little Single I found on bitmit is 15 BTC. You can get the 10Gh/s blades for around 4BTC apiece. Either I'm missing something, or the blades are cheaper...
15BTC for a 30GH/s Single?! The 60GH/s units are going for 20BTC last time I looked.
1 SC Single - 60GH/s @ 240W for ~20BTC + 0.5BTC for cost of rPi.
6 Blades - 64GH/s @ 450W for ~24BTC + cost of backplate, PSU, a dozen fans, and 8 port switch.
The BFL might be louder, but it'll use less power, take up less space, and is cheaper.