LA to SF is a little under 400 miles so the 1000 miles is round trip plus hair way back a second time. Superchargers is a little more than $0.20 ($0.28 avg, higher in Cali.)
On the Tesla site, the cost for 1000 miles is $72 for the 3, $84 for the S and $95 for the X. If you read the fine print, the free miles do expire but it is 3 years so doubt it will be too much of an issue.