Usually those are Chinese made starters and some are really good and some are not.. Check the return and guarantee policy of the supplier and his satisfaction ratings.. For that price difference, I would roll the dice.. The 1 GM probably shares a starter with a lot of small engines and your chance might be pretty good with this one..??
Saving $315 is never a bad idea. A starter electric motor is one of the simplest parts that can be found so some of these aftermarket units are good enough to provide years of service. What is the problem, worn brushes, failed solenoid, fouled bearings or shorted armature or coils? Have you eliminated possible voltage drop cause by poor wiring or connections? I would test just the motor part against a 12V battery to see if it spins freely. If it does then it would be worth it to take it to an automotive electrical shop for bench testing and repair. If you just want to replace do like kloudie suggests and check on the vendor's reputation and return policy.