If you're only willing to do 20 minutes, you're probably gonna have to live in the San Diego city limits. I live in North county and am not too familiar with that area. I wouldn't go any farther north than La Jolla. Pacific Beach or Ocean Beach area might be do-able, but the commute might be a deal breaker. You could look into going south to Imperial Beach. I have some friends that work at MCRD, which is right where you want to be. I'll give them a call and see if I can get some more info for you. Do a google maps search and look at the area around there and the sports arena. If price isn't an issue, there's always condos for rent around the gaslamp