For concrete and fences you really dont need hot water. Sometimes hot water helps with really greasy concrete, but we have used the heat maybe 1% of the time on concrete.
Are you just looking for a portable job like from home depot or are you looking for a tow behind rig or what? The truth is for what you are doing you can do decent work with a pretty basic unit. It won't last very long if it's a cheap residential unit - but will indeed get you started.
This sounds silly - but we run 2 person crews... 1 runs a $12k rig and the assist runs a $399 unit from lowes. While there is night and day difference in the two units, the little unit still handles a good 25% - 30% of every job. I think one of the biggest problems in using the little units is the perception it gives your customer.
Using good detergents can greatly reduce the work load of the unit too. Took me a while to succomb to that one.