I had good luck with craigslist, you can find someone just the same as if you were looking to hire someone as an employee. What you pay depends on your area, market, what you're charging customers, what kind of detailing your guys are doing, etc. I paid my guy around $25 - $50 per vehicle depending on what that vehicle was getting and he was mainly doing basic (non machine polish) and one-step details. If you're not familiar with hiring a subcontractor, do some good research about the laws and regulations of doing so, it's much different than having someone on your payroll.