To get Undercover Tourist's best prices you should sign up for the Mousesaver's newsletter. Beyond that they don't really offer lower prices. The Mousesaver's discount isn't large but every little bit helps!
The UT discount through MouseSavers is for park tickets, not hotel rooms. Booking through UT will save me $100 on 2 rooms for a 4-night say over WDW prices. It's not a ton, but I'll take it!
Sorry, I didn't read your post close enough to see that you were wanting to book a room. I'm pretty sure the hotel deals they offer are not fluid in price.