My husband & I will be driving from LA to San Diego on 20 Sept, as this is our first trip to USA we are unsure on where the best accomodation is in San Diego with a price range $60 - $80 USA per night.
Look forward to some helpful guides

Hi Tina: We just returned from beautiful San Diego, you will love it, esp. the weather. We stayed at an older, but very comfortable Comfort Inn on Ash Street downtown w/ a great Continental breakfast & friendly/helpful staff. A little out of your range at $95/night but for the location I believe it's one of the most economical. Enjoy your trip!

The price range you are seeking will limit your choices in San Diego. The Hotel Circle area should have a number of hotels at that price. They will most likely chain hotels like the Days Inn. Hotel Circle is centrally located near the beaches and downtown. The Old Town area is another place you should look at. There is a Ramada and Best Western there.

Since you don't have your heart set on a location, why don't you try bidding on priceline? I've used it on a number of occasions and have always been happy with my hotels.

go up the coast a little to Carlsbad and there will be plenty of places in your price range or less