135 spacing, right? There are a lot of lightweight 29er wheelsets if you don't need to run too narrow of a tire. I have the XT 29er wheelset on my mountain bike, and I think it weighs in at about 1800 grams. You could probably run 28mm tires on it alright. They can be found online for around 600 dollars IIRC.

You can also always get some nice hubs laced to lightweight road rims, too. American classic hubs to one of DT Swiss's offerings, for example. It just depends on what you want to spend.