As someone mentioned in a previous thread on dwolla (re your second point), you don't list two different prices. When the customer is checking out, you give a cash discount if you use dwolla (e.g. 3% off your purchase if you use dwolla to pay!).
If you're referring to RyanAir (and the other low-cost airlines), then they only offer free transactions on obscure payment types. From what I've seen the 'free' transaction type changes whenever a more obscure and impractical payment system becomes available.
They do that so that they can legally advertise lower prices that they charge in practise.
http://www.fdic.gov/regulations/laws/rules/6500-500.html#fdi...