Another thing to look at is the Gator vs Kubota. At a previous job, I used a Gator, and when you would step on the gas it would go at a slow speed and then "kick in". I always worried about tearing up wet turf or dew ridden turf even with the turf tires. Kubota's do cost more, but there are diesel models that can handle carrying the weight of 50 or 100 gallons. I don't know if they have the "kick in" like the Gators do.
It's tough to price applications at a set price. So you're saying if I have a 25k lawn and my neighbor has a 10k lawn it's the same price? I don't think so. Know your costs for the truck, fuel, tea, water, travel time, application time then you can come up with a price. Setting random prices usually leads to lost money very quickly.
As far as a recipe, what brewer are you planning on using? If you go with Tim Wilson's recipes are included..