The Official Blog for ADOM & Ultimate ADOM
How much will cost ADOM on Steam?
The final pricing has not yet been determined. Given the fact that ADOM will continue to receive a steady stream of updates I'm right now thinking about the "just under $20" range, but there are good arguments for lesser prices but in game purchases (of features like an exploration mode, *man challenges, etc.). It's a very difficult question and I'm also looking forward to see whatever Valve is going to recommend.
And seeing that games like Rogue Legacy also are priced 14,99 EUR I don't see why ADOM would be worth less.