I think there are sponsors on here that hire out coffee carts. I might be wrong but I know I saw them for rent on an australian site so there is a good chance it was a link from the sponsors section. If you can find them talk to them and ask them what setup they have and they might be able to help you out. I imagine most heat exchanger machines will do what you need.
Does your budget include the grinder and the cost of the cart or just the machine alone?
btw you can go up to 2400w on 10 amp. You may have read reviews of 10 amp being hopeless on the net. I think in a lot of these cases they were US reviews where they can only pull 1200w off 10 amp.