Another vote for boondocking.
Most of our camping is on the eastern side of the Sierras, so I can't help you with specifics, but there is plenty of boondocking on the west too.
I guess the only place I can name specifically is Shaver Lake. The drive is pretty steep and twisty and might not be fun depending on your setup. But the payoff is pretty good.
There are plenty of other places though. And if you don't feel like driving up into the hills, I would definitely look at Harvest Hosts closer to the wine country. Since we're talking about next weekend though, it's probably going to be cooler in the higher elevations.
I just looked at the map and it's about four hours from Travis to Shaver.
It's only 1.5 hrs up to Coloma in the Gold Country. We stayed at an RV park there (primitive) and it wasn't very expensive. You can walk to dinner and goof off in the river during the day. It's too late in the season for rafting since the river is so low now, but it's still pretty nice up there. There's also plenty of history nearby if you want to see Sutter's Mill, etc. Placerville is nearby too and it's a fun little town.
I got stuck up there in Coloma one summer when the DEF pump went out on my truck. The local Dodge dealer was really good and got Dodge to cover it under a courtesy claim, but stuck is still stuck. They had my truck for a week and my wife had to catch a ride back home to get back to work. Luckily I had my laptop with me and I could walk across the highway to bum their wifi at the coffee shop there in town. I've never drank so much coffee, but at least I didn't lose any work.
Long story short, there are lots of places out there. Some of them are free to boondock. Some are borderline free since you need to buy some wine to stay there (Harvest Hosts). And some are cheap-ish. The season is definitely over in Coloma, so I assume it's cheap to camp there this time of year.
Good luck.
