I hate to be a portable basher as I know they have their place,but sinking money into a heater is kind of a waste when you could use it for a down payment on a TM.
If you start talking with truckmount makers you may be surprised how cheap you can get a simple,compact,lightweight machine put together from parts they have laying around.
Matt at Crown cleaning supplies built a nice one 16/33 from spare parts for $2500 with out a heater. John at hotheatexchangers.com has had a used 18 hp briggs coupled to a used 33 blower that has been sitting on a rolling cart for 3 years. I'm sure he would love to trade it for cash. He also has old
prochem frames,dump tanks and probably repaired HX.
I guess my point is you might be surprised how cheap you can get a small tm made for if you shake the bushes. Probably for less than you have invested in your current set up. The only thing that seems hard to get cheap is heaters.