You absolutely need another job in order to fund a rescue. I've run one exclusively for going on 3 years now, but I'm putting my own money into it. Donations and adoption fees don't even cover the cost of feeders, let alone caging, meds and vet care. Lots of people talk about how they want to help abused and neglected animals but the sad fact is that most are just looking to get a new herp cheaper than they can at a pet shop.
I have yet to meet anyone involved in rescue that doesn't say the same thing but keep hoping things will change. Unfortunately, right now it's getting harder rather than easier in the US. In order to keep your non-profit status you cannot breed reptiles anymore and sell them in order to support the rescue. Now that I don't have that source of revenue I've had to turn most of the potential rescues away.