There are over 14K listings for aftermarket (chinese made) replacement extendable towing mirrors of Fleabay, and out of the 3 times I have purchased these for myself, or installed them for others at least a dozen times, no real complaints. The ones labeled "Koolvue" seem to be the best. $200 or less will get you a set unless you have a Dodge, and they can be found with the options such as heated, etc. They look exactly like the OEM mirrors.
GMFordDodgeOr you can go OEM and shell out $300, $400, or more per side.