There is a long waiting list for moorings in the San Diego harbor. There are a couple of cheaper marinas
down near Chula Vista that might be reasonable.
Sailing south to Mexico
from San Diego is easy, but bashing to windward to get back isn't so easy. And other than Ensenada (and I don't know why anyone would want to go there) it is a long way to anything nice in Baja California
If you are not a US citizen it will not be possible to federally document the boat in your name. You could set up a corporation to do it in though. But California registration
is available to non US citizens and will be fine for cruising to Mexico.
In any case prepare to pay California sales tax on the purchase
(unless you do an offshore sale
and keep it in Ensenada for 6 mo I think before you bring it back) and pay about 1% of market valueyearly in personal property taxes
Come to think of it Ensenada is looking better ;-).