Flight
Flying from PDX? Alaska Air offers super cheap flights. If you can manage it, come into SF on not the weekend because their lowfare calendar is absolutely terrific. Also, yeah, super cheap into SF.
Travel Note
You can do this, but should you do this? Probably not. This drive is a lot, honestly, check out Alaska Air first for hella cheap flights before killing yourself on this drive.
Train
BART and Muni are both great ways to get around the Bay Area. From SFO into downtown SF you can grab BART for relatively cheap. Muni helps you get around downtown (mainly down Market Street) with ease and is $2.75 for adults. F car: you can take this from Market and Castro all the way to the Wharf. A bit slower than Muni (which is underground) but has some brilliant sites (i.e. the Embarcadero) and is the same price as Muni. You might also experience some of the SF homeless so prepare yourself.
House Or Rental
Honestly, everything is expensive in SF, we know this, we live hurr. I would still suggest trying to find somewhere to stay within the city because travelling a long distance immediately following a wedding reception is never fun. Powermove: rent with some friends, split the cost, share a single bathroom, relive college life a little