Find your local VP Racing Fuel retailers and you can buy M1 racing methanol fuel. I think it sells for around $3 - $4 a gallon. My local shop in Belton, TX was selling me fuel for $2 a gallon but I think it's gone up to $3 a gallon. Mix in 50% water and your down to $1. 50 - $2 a gallon. I use distilled water so my cost per gallon is probably $2 per gallon. I bring four 5 gallon cans to fill up at a time. Forty gallons of 50\50 mix will last a while.
A pure water\meth mix will burn clean and probably leave your engine cleaner than running nothing at all. If you run washer fluid you may want to run straight distilled water periodically to help keep the engine free of any build up. Meth is a toxic liquid and known carcinogen so be careful when mixing it.
It's not worth taking a chance running a home brewed mix in an engine that can cost $10,000 to replace.