We are flying into San Diego in July. From what I can see, Advantage has the best rates for a rental car for 10 days. Has anyone used them? Are they reputable? I have no experience with them.
Seriously try Priceline. Google better bidding to get some tips on bidding, but I got a 6 day rental for a standard sized car for $18 a day out of LAX for late June. After fees and taxes it came to about $26 a day. Can't beat that. Rental car reservations can always be cancelled, so keep the deal you have. Try bidding (I low balled my bids starting at $10!) an amount each day since you have a ton of time until your trip. I only say this (if you are not experienced at priceline) is that once you bid, and it is not accepted, you have to wait 24 hours to bid again unless you change the size car you are trying to rent.
Anyway, when my bid was accepted they then tell you the company. Hertz accepted my bid. Priceline only uses the top 5 rental companies (Hertz, budget, alamo, National, and Avis I believe).
Just to let you know, the cheapest deal I could get was with my BJ's membership from Budget for $335 for the rental. I got it from priceline for $158 total. The only catch is you have to prepay on a credit card. Once you bid is accepted, you have paid for it. There are no refunds, but for an almost $200 savings, it was worth it.