Quoting on a job like this is very much a "How long is a piece of string" type job.
Weigh up the promotion aspect, the non-profit aspect, the connection you have with the owner, how much money you need to eat and sleep, what time commitment they will be working with.
For a single day, I have charged between $0 and $2,000 (I typically work corporate, so the money is there). For a single project (a day of setup/show, with a few hours of pre-production and a handful of meetings - any more than two personal meetings and the price starts to go up), again I have charged between $0 and $10,000 - purely for labor.
My average rate is $550 a day, walk in, walk out. Projects, $1,100. It's based on what I need, and also what my clients can pay though. Flat day rate is generally better than hourly, and for projects you need to be really careful with your contract, or you end up working on it for a month straight and not much to show for it...
For an idea of cost though - my rent is about 2/3rds my day rate a week. So I work 2 days a week freelance, and I am fairly well off. If I score a project, the rent is almost covered for the entire month. I also have to worry about public liability insurance, private health insurance, personal equipment insurance, food, transport, utilities, tax, accountants etc etc etc. So 3 days a week and all is golden.
Currently, I am full-time employed in a venue which is so much easier on the accounting.