To be "realistic" you MUSTadd up all your expenses and divide them by the number of runs made to determine a per run cost whether you are a poor part time team or a mega team. And you must include all costs.
Too many teams fail because of poor planning. They just add up the costs on a good clean run and think that is the cost to run the car. They forget about all the small things that are involved. And the more events you attend, the more the small things turn out to be very big things.
The biggest help to a small team would be to help them create a business plan and budget, then help them maintain the team. A poorly managed team will spend everything they have without concern for longevity, no matter how big the amount. I have seen teams that prosper on small investments and survive for years and teams squander millions and be out of racing in a short time.
You can run a pro car for as little as $3,500.00 a run but with that budget the first hiccup and the team is done. It takes an $8,000.00 per run budget to survive on the circuit full time, and you need to be very careful of every dime spent. To be halfway competitive, it takes $15,000.00 per run. To be in the hunt you must be prepared to spend $25,000.00 to $40,000.00 per run.
These are all inclusive numbers. You might have a streak that you run for less, but you have to be prepared for that streak when it costs more per run.