This sounds like a sole trader venture, the only way you can get money is self investement,
You may need a loan, keep costs to a minium spend a lot of flyers and marketing, to advervise first.
Got to the bank, for a loan, with a projected costs and projected cash flow in your business plan,
I think with is a big amount of cash at the start, but then it can make pure profit down the road.
How about charge in bulk prices, like not single washes, but 1 wash=$5
But 10 washes= $30 this will increase sales costs at the start, and generate money return before interest kills you on your loan.
Hope that helps