Better than that, start a private tutoring business......really the associated costs are minimal, paper and a printer, private tutors are typically paid in cash.....I run a music school, there is no way to know how many clients I have and how many have paid, unless they pay by check, all those paid in cash can be kept from the taxman, but it could work the other way.....you could have no students but an extremely profitable business and who would be able to tell....great thread!