Have now financially committed to Anza-Borrego - cheapest way having waited until now turned out to be flying there with Southwest and back with Jet Blue. I don't recall quite what the fares I was seeing a few weeks ago for the round trip on Orbitz were but those flights appear to have filled and the round trip can't have come in much cheaper than this. Plus this way I don't have to get to the airport in time for a 6am flight.
I'm still in the market for anyone who wants to camp at the meet site and share a rental car from San Diego airport - my flights will be arriving around noon on Friday and leaving at 10:20pm on Sunday.
Addendum: at least, if no one wants to share a rental car with me, it appears San Diego is a dirt cheap place to rent a car - first time I've ever seen a base rate of $10 per day and the additional fees don't even come to much.