how hard is it to replace a hub and rebuild the wheel.
If the wheel is still fairly straight then it is pretty easy. If the wheel is already a bit wobbly then truing it will be hard. It is much easier if you have a wheel to hand to copy once you have taken your old wheel apart. Go for it!
It’s ok, you can always take the middle route, lace the wheel yourself but have the final tightening and trueing done by a bike shop, which is cheaper and more fun then getting them to do the whole thing. If the rim is bent it will be more tricky to build it to pull the rim straight again. Look for Sheldon Brown’s site, he has a great wheel building tutorial
The basics of building are very easy to learn(im being taught now). But it takes alot of practice to get it right every time.
the rim is stright but the hub is bent
Turn all the spoke nipples the exact same number of turns. Keep tightening all nipples identically until the general pitch of the twang is right. Then tighten individual ones that are lower pitched. Then put the wheel in the frame and adjust out the remaining wobble. If all that fails, take it to a bike shop.
john’s link to sheldon’s site is all you’ll need.
my first wheel rebuild took me about three hours. ride your newly-built wheel for a few miles, then take the tire off and re-true the wheel / re-tension the spokes as the nipples may need to “settle”. this will give you a stronger wheel.
if your spokes are especially worn / bent / stretched / etc. it may be a good idea to replace your spokes. if you don’t want to replace your spokes, at least make sure you re-use your spokes in the same position as before (i.e. inside spokes remain on the inside, and vice-versa). otherwise you may weaken your spokes even further.
the process itself is tedious, but it’s the best way to learn what really goes into making a strong wheel… and it does take lots of practice to become efficient and effective, but everyone’s gotta start with their first wheel!
cheers, and good luck!