A couple of years ago, I bidded on the 4* Carlsbad area and have gotten the Sheraton Carlsbad Resort and Spa for $130/night during a peak summer month. This year for our upcoming August trip next week, I had no such luck. I had to go outside the Carlsbad area into La Jolla. Got the Marriott La Jolla for $108. Not bad, considering much of the 3* and up hotels in the La Jolla and Carlsbad areas are going for close to $150+/night.
If you're going during the Fall, it's not peak season, and you'll get much better Priceline deals.
But beware that a lot of hotels on the Priceline hotel list charge for parking (in La Jolla, some have $20/day charges). You may want to look into the Homewood Suites or Residence Inn in Carlsbad, which may offer you free parking and complimentary hot breakfast. Both hotels may offer rates that are comparable to Priceline.
BTW, I use both betterbidding.com and biddingfortravel.com.