Ouch!! How expensive was that lesson!!!!
Under a $100. Just used some harbor freight units, think they were running about $20 when I bought them. Onsale for $17 right now: http://www.harborfre...ster-38944.html
I'd rather have used these for a better strength/built quality (on appearance) but I was going for larger over the gravel. As it is it still doesn't roll well on gravel, digs in/turns wheels, so some plywood strips would be needed under the wheels to make it happen. http://www.harborfre...ster-41565.html
The rest of the cart was just a cheapie quickly slapped together form some 2x4s to test it out, I'd built a better/stronger one for long term.