You might try looking for a used Bob trailer on Craigslist. It is really nice for hauling groceries and it tracks behind the bike so you won't even notice it is there. Because it only has one wheel, it doesn't work as well for large loads but for compact loads, like groceries, it is great. The big advantage of the Xtracycle is your load is located between your axles so it rides in a VERY stable way. You will notice when you have really heavy loads on regular panniers, you will get a fishtailing type of motion.