I can't really recommend anyplace that would be worth stopping over, but if you just want to find less expensive accommodations, there are loads of motels in the Fairfield, CA area.

You might look at staying in Murphys. Murphys is the heart of the Calaveras County Wine Country.

http://www.calaveraswines.org/

There are some excellent wines made in this area and they are more reasonably priced than Napa or Sonoma wines. There's also the gold country attractions in the area as well - Columbia, Mercer Caverns and Calaveras Big Trees.

Murphys is a 2.5 hour drive from Curry Village.

Don't even need to go up as far as Fairfield-
Vallejo has lots of budget friendly hotels along
I-80-then you can head up Hwy 29 into Napa County.
Or over to Sonoma County via Hwys 29 and 12.
Sonoma is a big county-any place in particular
you were thinking of visiting in Sonoma County?

R5

There are motels in the town of Napa that should be less expensive. A couple of Best Westerns and Motel 6. No need to sleep some where on the way.

Are you planning to drive straight through from San Francisco to Yosemite and not stop along the way?

If so, then Yosemite to Napa is only about 20 miles more than SF-Yosemite.

Both trips are almost equidistance and should take you no more than 4-5 hours in non-peak traffic hours.

If you must stop before Napa, then R5's suggestion of Vallejo is an excellent one. If you're going to stay in Vallejo, where the hotel rates are much cheaper than in Napa, then try to find something right around Six Flags or the I-80 (Columbus Parkway) exit area. Don't get a hotel in other areas of Vallejo, not safe.

We love Napa but really love the cute little town square of Sonoma. It's easily drivable from Yo in half a day (mid-day) - so just go for it.

Just keep googling and you can find some good deals in the Napa/Sonoma areas.

Thank you all for your suggestions. We are actually staying in Groveland the first night before we stay in curry village Yosemite. It should be about 3 hours to get to Groveland. I like the idea of staying in Murphys and visiting the Calaveras Big Trees. I'm thinking we could drive from Yosemite to Calaveras then stay the night in Murphy's.

This way we could drive to Sonoma/Napa, maybe stay in Yountville for two nights . It looks like it would only be about 2 and 1/2 hours to get there from Murphy's. That brings us to Saturday.

We could spend the last day, Saturday in San Francisco before flying out Sunday morning.


Problems:
We fly out very early Sunday.7am. Should we sleep near the airport.? If so, what should we do with the car on Saturday while in San Francisco and what do we do with our luggage all day Saturday?

Second question? Any specific suggestions on where to stay in Murphys and Yountville? Thank you so much in advance.