John, if your budget won't stretch any higher you'd be MUCH better off buying a second hand machine of a much higher spec than what you can get new for £1500.
That sort of money is going to buy you, let's be honest here, a crap machine. That crap machine will then depreciate in value and you'll not be able to sell it for anywhere near what you bought it for. You'll probably get fed up with an underpowered machine very quickly so you'll experience the loss in value over a short period. Not good financial sense at all.
If you buy a good machine second hand for £1000 you could sell it again for roughly the same amount, or only a bit less if you keep it for a few years. Once they get down to a certain 2nd hand value they will stay there or thereabouts.
All a machine contains is vac motors and a pump, the more performance the better. The Alltec Aqua has a 70psi pump and ONE vacuum motor, it's puny little puddlejumper. For many years, two vac motors would have been considered the minimum but three vacuum motors is now becoming the norm. triple vac machines are available from alltec, and also cleansmart and Solution in cornwall (i'm thinking theres another but can't recall who sells it at the mo)
The shurflo 135psi pump is found in a lot of machines, I wouldn't go any lower than this. Lots of portables now have much more powerful pumps that can go up to 500psi or more.
Sorry if it sounds liek I'm preaching but you need to think bigger and longer term with a machine, it's the absolute core of your money-making ability!!
