regarding costs, I assume it's as expensive as the other spas at WDW - that is to say, very.
However, I don't know what sort of spa costs you're used to in the UK. Perhaps it's relatively cheaper to what you could have at home. I live in a country where spas are common, very heavily used, and extremely reasonable. So for us, the WDW spa prices are sky high (not surprising really - everything else at WDW is sky high).