Remind them that they are NOT hiring an employee.
Tell them You are a legitimate business with all the expenses required to be so (insurance, taxes)--- tell them this even if not true--
tell them there are also additional hours worked off site to run this business, such as: marketing, maintenance, bookkeeping, education, purchasing.
as well as additional expenses such as: equipment replacement and repair, vacation, retirement, health insurance, beer.
Or keep it simple and tell them-- your hourly rate is barely enough to keep you interested and keep it at that.