Shop around for some reasonably priced disc mtb hubs and 700c wheels and build them up, or have an LBS do it. A buddy/wrench at my LBS has a Karate Monkey set up w/ mechanical discs and 2 sets of disc wheels. One gets a set of 2.3" WTB 29er mtb tires while the set used for commuting to campus/work has a set of 700/25 Contis on them. Both sets are disc only and he laced them up on the cheap. Less than a machine built pre assembled pair from the catalog even after his shop discount.