This one is rated 800 lbs and on sale from Sears for $49.99. It has pneumatic tires and it's a convertible. Save more with your SYW points. I happened to have $10 freecash, so $40 for me. No shipping option available so YMMV. Also, 15% back in SYW points.
[below expired] Amazon's price is now back to $114.
Similar one from Amazon with "Puncture proof wheels" going for $49.94 ships in 1-2 months. According to camel, this is the lowest price ever. Average around $100.