There is no proper price to charge as a percentage of purchase price. The resale market and the rental market define it for you.

The current rate for SFR in San Diego is in the 3.5-5% range. E.g. a ~500K house in Clairemont rents for $1700 per month or $20,400 per year. Compared to house value thats about 4%. (I use Clairemont because that area has been very near the SD median for the last decade).