In theory, self-driving cars should all perform equally within the same range and, probably, within the same manufacturer - you'd assume they'd put the same system into each car, and keep it updated to their latest best effort. In fact, this principle should perhaps be enshrined in law.

Therefore, individual owners do not need to be taken into account. Simply calculate the average cost of an accident and multiply it by the likelihood of that maker's system causing a crash, and send the owners a bill each year.

It doesn't even really need to be determined who "caused" the crash in each specific instance. It should be plainly obvious, statistically, which self-driving systems are more likely to be involved in accidents - premiums would be weighted to reflect that, and this would encourage a virtuous cycle of improvement incentivisation.