I used to ride about a 100 miles a week, in my fit days;-) I was one of those whining about my butt, wrist, neck and back after a few miles. Then I switched to recumbent cycles and, like transition, I'll never go back. As Laura suggests you may want to find a used one but there is simply no comparison to cycling in the recumbent position. Sort of like riding a lawn chair. I ride a Bike-E and the manufacturer is out of business with a bunch on the used market. You might consider trying a recumbent out at a cycle store that sells them.
The lowest cost options are to get a shock absorber style seat post or a wide gel seat for those common double diamond, up right, "wedgie" bicycles.
Happy trails!