It is still available with some resellers such as the one i gave you (https://bitcointalksearch.org/topic/closed-antminer-s1-by-bitmain-in-los-angeles-ca-usa-new-price-511002)
or on Amazon (http://www.amazon.co.uk/AntMiner-S1-180-standalone-unit/dp/B00HNTUC2M)
Actually, most devices ROI is about the same, but the S1 is a middle-class one which isn't expensive as others and provides a decent hashrate.
Use this calculator: http://www.alloscomp.com/bitcoin/calculator