I built one a couple of years ago. Didn't cost me hardly anything (except for a SS
coin box) as I already had the parts (timer, coinmech, solenoids), etc. Made my own signs.
See it here
http://www.wallywash.ca/Detail_Area.htm
I think I'm the only one around who does this and so people don't understand the concept. So it doesn't get used much...but its just another revenue source. Like an air machine (that does way better and requires nothings).
I always use the same stuff I buy in bulk from a company that supplies lube shops. The come by and fill my 55 gal drum directly once a season.
I enjoyed making it with my son and he buys the fluid and makes the profits. But his pop machines does much better.