"but once the insurance premium of a normal car skyrockets above what you can afford (it won't take long) that will be that."
Why would the insurance premium skyrocket? There is no monopoly, the premium is largely based on the risk and free market. For the premiums to skyrocket the risk has to skyrocket, If introducing self driving cars on the roads increases the risk of collision, noone will do it in the first place. Nor the prices of cars will skyrocket, so the risk stays roughly the same, hence the insurance premiums.