You could build one for a lot less money....the only problem with that tho is most architects specifie Doff or ThermaTech.
All the fixtures and fitting need to be capable of withstanding 150c. Most off the "shelf hot boxes" only get to about 90c. When you start making steam strange things happen to hoses ,fitting,trigger assemblies!
It really depends what you want the heat for ...if you are washing wagons,diggers the Thermatech is not really the right tool.