I'd suggest you give a call
With that budget you'd be looking at Numatic, Karcher machines. Fine in their own right but comparing to a powermax worlds apart. Don't forget you would need hose, wand, hand tool, chemicals and most important training and insurance. Low powered equipment will make this job very hard work and honestly you are really under budget and in most cases those that start off this way tend to regret not starting with better equipment. There are a lot of suppliers around like Solutions, Cleansmart, Prochem, Restormate and Alltec all of whom I have dealt with and all give excellent advice and service and some offer free training with machine purchase.
I would start by asking your customer base if they are interested in an additional service and monitor response, if there's a market for it then take the next step.