If you can true a wheel, the building it part should be pretty easy, I learnt by a combination of Jobst Brant's book, Sheldon Brown's site, and a few other web sites. not had one fail on me yet.

For Aftermarket / complete wheels, I think that these get mentioned a lot as being cheaper; is because they are. I don't think that any wheel I have built has been cheaper than a Aftermarket one, but I know that I built it, and enjoyed doing it.

For the quality of factory wheels, it's years since a bought a complete bike (machine built wheels), so don't know what the quailty of them will be, but would go with the more you pay, the better they are; but I have bought Fulcrum, Mavic, Rolf and Shimano aftermarket wheels, ridden all them hard, and never had any need to true any of them. If you were buying a handbuilt replacement, that should come already correctly tensioned, and not need any adjustment (if the builder knows their stuff).