We just did some looking into costs and found this government page showing prices for green power programs from utilities by state: http://apps3.eere.energy.gov/greenpower/markets/pricing.shtml?page=1. The typical range seems to be 0.5 cents to 6 cents per kWh.
We also got a quote of 0.2 to 0.3 cents per kWh for RECs. What are others finding? RECs seem consistently cheaper--are many people choosing local green power anyway because it seems to have more integrity?