If the rim is bent, you will need to replace it and most likely all the spokes. If the hub is ok, and the cassette is ok, you can probably keep those. Around here labor to have a wheel re-built is about $80 - $100. Parts depend on what spokes and rim you want. If the wheels are low-end factory-built to begin with, you might be better off with a new hand-built rear wheel. For a tour, you want a wheel you can rely on. Don't cheap out. Get the rest of the bike inspected for damage, too.