First of all I assume you have all the necessary licenses or whatever needed to set up a tattoo business.
I do not think that the autoclave is the best thing to save money on. Better get a new one from a reliable source - it also will have a manual. Have it serviced according to manufacturers recommendations. In case somebody sues you you can prove that you have your equipment in excellent shape.
Imagine yourself standing in fron tof the judge and he asks you if the tools were sterilized and you tell him:
"Well, I put them into the pressure cooker" next thing he will ask if you then chose some needles from your mothers sewing box to do the tattooing or a fork from kitchen drawer.
I do not want to speculate about other methods as I am not tattooing or have any tattooos.