Your costs will be determined by your expenses, not someone elses. If you were in my neighborhood in CA. you would pay 5k per month for a 2 bay gas station- a closed one with no tanks running. What is the wash bay like? Do you have a water reclaim set up? If not, you are asking for real trouble. You will need something in place and approved- a clarifier or separater meet the EPA, but some cities will allow other methods. I suggest you become involved in your community through the Chamber, sponser youth teams, etc. You will really need to put a business plan together. "Affluent neighborhoods nearby," does not make money. What is your market? If you don't know yet, than you don't have a plan. There are some great books out that deal with marketing, finding your market and directing your money to getting your market to make you money.
I wonder if you can purchase something? I would rather buy a property than rent since the monthly payments are much less than a rent payment. Plus, you own and then will build appreciation in the value of the property. Heck, work for three years, make a positive gain, and then sell for triple net!!!
The E-Myth Revisited...read it!
Think about car flow. The more you have to move cars, the more risk. How much insurance will you carry? What's the customer area like? Will you sell retail items? What software are you using to track customers? Sales? How often will you send out mailers? Will you do add-ons...tinting, PDR, etc.?
Just some well intended thoughts.
Rob