They haven't exactly done it all on their own like people like to think. The giant house they live in was completed by Discovery who found people to donate their time. The Duggars started the house but couldn't finish it, so Discovery footed the bill and found people to work on the house for free. The house was furnished, decorated and stocked by Discovery as well. They may have been debt free, and doing OK before Discovery came along, but that was 7 years and 6 kids ago (they did their first Discovery special in 2004). Discovery probably pays them at least $50,000 an episode I'd guess, if not more.