The due on sale clause is an option they give themselves. They can choose to enforce it, or not. It's not like they hold a meeting to decide if they should call the loan due, every time they find out the deed has changed hands. Far from that, actually. Loans are rarely called due in full on deed changes, if the insurance and mortgage payments are kept up to date, at this point in time. If you do it right, it doesn't necessarily have to cashflow, either. That's just a perk, and more cash in your pocket every month.
You're looking good on transfer taxes in Cali, also. You only have small local taxes. If I were to file a deed on a 125K home in Delaware, I would need to bring $3750.00 to the courthouse with me, out of my pocket.
FYI - Get added to the sellers fire insurance, if you decide on a sandwich lease. If your tenant burns the house down, guess who they're going to blame.... (ive said this before, but its important)