Looking at going to SF area for a week plus including Labor Day. I'm thinking we'd drive up to Napa area for two nights and do some wineries (yes, "half" of us have been there numerous times) -- the other "half" of us, not at all). I'm guessing Labor Day itself would be a horrible day to hit wineries? And maybe hard to do a place to stay for Monday and Tuesday nights only -- or would that not be a problem since it's hardly still the holiday weekend?
Another option would be going a week earlier and coming home Labor Day weekend, which means we'd be in Napa area on Monday and Tuesday nights the week before Labor Day. Are the wineries open on Monday generally?
Meanwhile any recommendations for a nice place to stay without breaking the bank -- not looking for the "spa weekend" experience -- a nice place for $200 a night would be great.
I've stayed at The Vineyard Country Inn near Helena a few times which was nice -- I think now about $300 a night, but maybe less mid week.

I don't know about wineries hours. Check their web sites. But I can say that Labor Day weekend will probably be a terrible time to visit the Napa valley because of crowds/traffic. A week before might be better. If going on Labor Day weekend, make sure that you are not returning to the city on that Monday.

We had to attend a wedding in Sonoma Labor Day weekend. They were requiring a 3 day minimum. Since you are coming in at the tail end of the weekend, you will probably do not have to worry about this.

I would avoid Labor Day weekend because, to my mind, Napa is more than crowded enough on a regular weekend. We usually try to be in wine country Monday through Friday for that reason, but I am not certain how many places are open on Monday--we usually travel on that day. There are so many wineries in the Napa Valley I can't imagine you'd have trouble finding any open on Monday, but again, I'm not certain...

Most Napa wineries are open 7 days a week. Expect to pay a pretty penny for your wine tasting.

This link should give you a bunch of information.

http://napavalley.com/?gclid=CM7G7vyv8LYCFSSCQgodeVUAbQ

Monday of Labor Day weekend is much saner than Saturday or Sunday. You shouldn't have problems getting a room. Tuesday will be even calmer. As stated above, just stay off the highways leading back to the city.