There are some bargains to be found in used motors.. I try to keep several spares for machines as backups, and for future projects.
Buying new motors isn't often a consideration for me, but I would if desparately needed. A used 2HP 120/240VAC flea market motor cost me only $35 a few years ago.. a great Westinghouse ball bearing, air compressor rated (start and run caps) in good condition.
A good alternate plan might be to find a variable speed AC or DC motor setup.. they're a great upgrade for any lathe.