Don`t underestimate the difference that tires make- it can be huge. If I understand correctly, you want a second wheelset for each bike to mount up with skinny slicks, then just swap the whole wheels rather than changing tires every week? That`s viable too- just obviously costs more. There are certainly wheelsets available. I`m not sure what`s out there for the 29s, but Mavic Crossrides would probably fit the bill for the 26 inchers. They`re cheap and relatively light. I don`t think I`d trust mine on the rough stuff if I were bigger, but they ought to do fine on an unloaded road trip for anybody. There are lots more out there, I`m sure- just that I know about the Crossrides. If you want to keep the cost down, I`d suggest just buying tires first and see if that does the trick for you.