A couple points of clarification for the conversation:
If you are looking for a cart, later models like the 7 and 10 tend to be more reasonably priced than the 80 the Troy mentioned in his great post. I picked up a nice worker quality 10 for $100 and a like new 7 for $120.
Can you please explain what the difference is between 7, 10, and 80 carts are? Is it differences in sizes? I'm not familiar with the different sizes, so how do I determine what size cart I'd need? I'd really be only using the cart for maybe leaf clean up in the fall, or possibly helping to carry mulch or shrubs in the Spring. I'm thinking the biggest available, but not something too big that the tractor wouldn't be able to handle. Recommendations?