I wouldn't pay more than $140 for a girl's. The boy's are worth more. If you keep on the lookout on Craigslist and check ebay local auctions so you don't have to pay shipping, you should be able to find one for less. Local Ebay is the best because you get the bike for $60+ less than anyone else, so you really get the upper hand for bidding. I picked up a nice one for $50, the seller did spell Scwhinn wrong though....I mean Schwinn.
Keeping in mind that some people call ANY spider bike a stingray, especially if it has a Schwinn frame, if it actually is one in salvageable condition, that's a bargain. Heck, if it's just an old kid's bike in working order, $30.oo is OK.
If that seat's original, and in as good of condition as the pic shows (kind of hard to tell, small pic), the seat is worth a bit more than $30. Original (non flowery girl) seats can go up over $100 on Ebay.