I’ve bought some stuff from Boats.net, best prices and selection for Yamaha parts I could find online. You have to know what you’re looking for though, it’s not always easy to decipher which kit, etc comes with what.
Also recommend Charleston Marine, not necessarily super cheap but they usually have pretty good prices, very helpful, and are local. Depending what you’re getting, may be worth a trip - shipping can really eat up your savings at the online places pretty quick.
I get my parts from Chris<Charleston Marine> as the advice and guidance is well worth it when I consider freight and ease of returns. If I mess up its the best deal.
He generally will diagnose and sell you what you need not necessarily what you think you need which in my case is good.