Finding a place to stay in San Diego certainly isn't difficult and hopefully with my local knowledge you can find a decent place and save money at the same time.
In my opinion you have three options. You can stay at a snazzy downtown San Diego hotel near the airport, a moderately priced hotel in Hotel Circle (Mission Valley), or a really expensive La Jolla area hotel with easy access to the water and incredible views.
Downtown San Diego is about 20 minutes southwest of Hotel Circle and Hotel Circle is about 30 minutes south of La Jolla. If you are interested in taking a dive boat out of Mission Bay you will only be a short 15 minute drive away if you stay at Hotel Circle. Similarly, if you plan on shore diving in La Jolla, you will only be 5 minutes away if you stay at a La Jolla area hotel. For any diving option a hotel in downtown San Diego will put you the furthest away.
Since I'm a local San Diegan I haven't had many opportunities to evaluate local hotels and I have provided the google advertisements below to give you a head start (since they are supposed to provide listings if I place them on a page about hotels). As always, if you have questions feel free to drop me an email.
You may also want to visit La Jolla Beachfront Hotels offering great rates on over 50
La Jolla Beachfront hotels. http://www.lajollabeachfronthotels.com/