Stickie,
I would definitely give Mansion exchange a try. The only thing to watch is that you need to email them ID to make a withdrawal so make sure the address you give them is the same as what's on most of your ID. Once you go through that (unnecessary IMO) charade, the withdrawals come fast and easy afterwards.
A lot of times you'll find it's like a super reduced juice shop with lines as thin as 2c sometimes. Of course sometimes there's no offer at all on one side...weekends are busier (and therefore better) than weekdays it seems.
To add to monicus' point, if you see something you like and you want to bet $300, say, if the amount shown is more than $300 you can go right in and make the bet immediately and it's yours. If it's less, say $150, you can bet it for $150 and then see what's "underneath" it. It may be 1 or 2 cents less for a larger amount so you can bet your other $150 at a slightly worse price. Alternatively you can insist on your price for the full $300 in which case you get $150 right away and the other $150 appears as an offer on the other side which will become a bet if someone snaps it up.