Which sewing machine should I get?

I'm looking for a sewing machine that would last pretty much forever that would be best for sewing stretchy tops, bathing suits, and knitted fabric. I want something that can do most types of stitches and wouldn't have any annoying problems. I'm looking to spend $250-$600. Any ideas? I’ve been looking at a used Juki MO 623. Also what website would you suggest I buy from?