With Winter approaching, I am looking at turning my eldest MTB into a winter commuter and also a shopper bike with panniers and a rack to hopefully carry some reasonable sized grocery loads. I need the rims replacing anyhow, but is it worth reinforcing the back wheel or will a standard MTB wheel be enough for a heavy rider and a heavy load?

Is reinforcing/rebuilding a wheel going to cost lots more? (never had a wheel rebuilt before).