I have always wanted one of those balance/stability/exercise ball things. Bad thing is that you cant find many of them that will hold over 250 lbs. I've had a couple and never used them because I was over the weight limit and was terrified that they would burst, and I've heard stories about people getting hurt pretty bad from that happening.
Well guess what I found and ordered yesterday...yep, a ball. Not any ball though, a ball that is approved for weights up to 600 lbs! Found it on the Walmart website. It's an 'Altus Be Fit Look Fit 75cm Body Ball with 2-lb. Sand Fill'. The sand is for stability for when you get up after you've been sitting on it, so it doesn't roll away.
I promise that when I get it and get it set up, I will post a comment to this thread to let everyone know what I think.
Edited to add---And it was less that $20!
Something I found...
's for you!!!! I am glad you were able to find one you could use. I REALLY want an eliptical, but unless magic happens and my husband finds a job I will probably not be able to get one!! But it will be okay because I have shoes and the pavement, and one way or another I am gonna lose this extra person!!!! 
