They can be hard to keep cool in hot weather - the cabs block the radiators. The cummins is known as a 555 "triple nickle" and aren't a great engine. Neither are the 3208's or the 6v-53's which were the other two factory options. I repowered two tms 250's to 8.3 cummins and that was money well spent. Mine were both 3208 powered originally, andthe 3208's just wouldn't hold together hauling 50,000lbs around in my hills. I've driven one that was 5.9 cummins powered and it wasn't up to the task.
The tms 200's are a stout crane, I still own one, and ran it today. The 80' main is just too short in a lot of places, you'll get good at swinging jib. The tms 200's don't bring much $$$, to me the two man cab, and if its 24v - and if its coles electric, all makes it worth even less $$$$.
I'll take my tms 200 over my national 1300 boom truck any day, unless I have to have the 95' main, or have to drive a hour plus away. The boom truck isn't built like the truck crane is.
Even if its really cheap, you still have to upkeep the engine trans rears tires and all the seals, and insure it. If it hasn't been being used, its a project. Then it comes down to if you have time for a project, and if its a crane you want to own after you get done with the project.