Lucker52 - You said "reasonable". I would suggest Pio Pico RV park in Jamul. It is a quiet area that is a short drive to Chula Vista. The beach might be 12 miles. City of San Diego 15 miles. it is a Thousand Trails Park. Even if you are not a member they will rent you a site. Price should be reasonable for monthly rate. They are doing lots of upgrades at this park currently. They have several very nice pools, on site restaurant (limited hours), people that run it are very nice. It is security gated. This is in a quiet area. Close to town but more like out in the country.
Not as nice as Santee Lakes or Chula Vista RV parks but way less money. Campland by the bay is very expensive. Someone recommended Guajome County park. I have stayed there. A long way to San Diego. That is way up in North County. Far closer to San Diego is Sweetwater County Park. Sweetwater has far and away much better sites than Guajome. I have stayed at one site in Sweetwater that had a peak of the ocean (distant view 10 miles away). I don't know if Sweetwater has long term rate. Pio Pico way quieter than Sweetwater.