The address you provide is not complete, so I can't tell if you are viewing a listing or a notice of sale (foreclosure). If it's the former, contact the listing agent or get an agent yourself.
If it is the later, that amount is probably only the amount owed on the loan. The notice will state the date and place for the auction. The lender will no doubt bid the entire amount owed to it in what is known as a "full credit bid", and you are free to bid over that amount.
Given the small amount, it is likely that this is a foreclosure on a second or third deed of trust. That means that there are loans with superior liens on the property. If anyone buys the property at the foreclosure auction, they take it subject to the existing superior liens. That may or may still be a bargain. You have to find out the amount of the superior liens to make that evaluation.
Of course it should be said that buying property at a foreclosure auction is a very risky proposition. You will not have any disclosures, you will not be able to inspect the property prior to purchase, and you will have to deal with the occupants after purchase.
The reality is there are no $20,000 properties in San Francisco.
Jeff Woo, Esq.
Sedgwick, Detert, Moran & Arnold LLP
Complex Rental Property Group