Taking financial shortcuts is the WRONG reason to choose maternal incubation, IMHO.
If someone can't divy up the money for an incubator and thermostat, they probably shouldn't be breeding, as they also wouldn't be able to afford the vet bill if their female were to have any issues, like egg binding and need vet care to save her life.
Yes, you need to control temp and humidity, but it's much harder to do with maternal incubation.
I've chosen artificial incubation, because I know that the temps and humidity remain constant, and I can't imagine having my females be off feed for 2 months after they lay. If you've ever seen a female after laying, you'd know what I mean. I'd rather my females start eating and getting good body mass as soon as possible, for their health and well being.