A set of remanuf. calipers will cost you about $100, the backing plates will run $60 - and that's just getting started - hubs are $80, rotors about $80, then there's brake lines, etc. Yes, it's worth a lot more than what it's going for now, but I'd check around & see what you can buy it for retail, then decide how much you want to bid - and don't bid any more than that. And don't forget - a lot of eBay sellers make their $ off the shipping since eBay doesn't charge a percentage of that.
And I don't know about posting a good eBay find here while it's still up for auction (unless of course, it's you that's selling).