If it was that easy I would be building a similar machine to a Prowler. But a quick tot up just shows how daft that would be. Blower £900, Heat exchanger £700, Engine £900, Pump £400, Hoses, rough guess, £120, Guages, pressure regulator, Solenoid valve £120, Then you have to have frame which is lazer cut then welded then powder coated. I doubt I could get someone to make that to the same quality for less than 5-6 hundred if not more. Theres getting on 4k then you have the labour costs, marketing, overheads and Profit. Just wouldn't be worth it.
Thats not to say building one yourself is out of the question. I think it would be relatively easy if you had some basic skills. It probably wouldn't be of merchantable quality but would do the job. But as Paul says probably better off earning or marketing.