It's really hard to pin down values on Yamaha stuff of this era, although the most similar bass I can find on eBay to this one did significantly better than $275. It's really all about who's looking that day.
I would personally trade the Squier off in a heartbeat for this, but I am a total sucker for Yamaha's necks from that particular era (I own three 500 series Pacificas and two 1200 series Pacificas, all from '89-'92 - and just had a custom Tele built at some expense *around* the neck profile on one of my 521s). So I'm pretty biased.
But yeah, this is one of those trades you'd best only make if you like the gear you're trading for. You can probably get what you "paid" for, maybe much more, but it's not as easy a guarantee as the Squier.
(edit: and yeah, it should be a really nice bass / instrument if it's not been abused unduly. Yamaha don't make no junk.)