While the price of S3 has not been announced yet, the anticipated price is likely to have a similar GH/s/BTC to the current market price of the S1. As the S3 hash rate is about 2.5 twice that of S1, the price is likely to be proportionally higher. The biggest advantage of S3 is in the relative power consumption, where it clearly beats the S1. If you get free electricity that wouldn't matter to you. There are second order issues like cooling needs (advantage to S3 on a per GH/s basis). You may also consider delay until supply (S3 is brand new, there is huge interest, it make take some time until deliveries start and actually happen). There is also a potential issue of 'infant mortality' issues, firmware/software bugs etc. (s1 had 3 firmware releases, a few h/w versions etc). Today the S1 is stable and mature. Mining difficulty changes all the time, so in bicoin mining time is of the essence. In my opinion, get a cheap S1 today, later either upgrade it to S3 or 'down-volt' it to improve energy efficiency (only if you pay for electricity).
('Somebody' just cancelled a S1 purchase from me, and I'm actually grateful...
Cheers
