I am asking for 275 HBD a day for a year. I calculated the price to be about 100$ an hour. So I will be spending between 15 and 20 hours a week on it

If proposals all have an About clause would that not solve the issue. If the proposal is based on 275 HBD equaling $2000.00 dollars a week, then why not a system to peg the requested HBD to a Weekly dollar amount. If the price of HBD goes to up to where they are receiving $2200.00 then simply reduce the amount of HBD for that week by 10% to the individual. Likewise if the price declines and they are only receiving $1800.00 then simply increase the amount of HBD to the requested dollar value. They still receive the amount they needed in dollar value of HBD.