I've used both of these sites for different projects but I probably wouldn't hire a copywriter on either. I think you're better of finding a copywriter with experience in your niche.

You can find them anywhere from $300 up into the tens of thousands. One of the best copywriters I've outsourced to recently was someone I found in the Warrior Forum for $450.

PM me if you'd like me to connect you with him. I think he's raised his prices since then but he's still a great bargain for the quality work he does. I could also show you the sales page he wrote for me if you're interested let me know!