There are some commercial units I saw down in New Zealand, for small business auto shops, wall mounted, high pressure, not Lowes/Home Depot consumer crap.........
don't know the costs, but you get what you pay for, $300 isn't much when you're talking quality motor/pump/hose/wand/tips.
http://www.pressurewashersdirect.com/Pressure-Pro-WM-EE2015G-Pressure-Washer/p1550.html
buy it once, buy it right, but maybe a cheap disposable Autozone or PepBoyz unit is what you want/need for only $300
http://www.pressurewashersdirect.com/power/wall-mount-electric-pressure-washers.html