Napa is not a budget trip. There are ways to cut corners, however, you can’t cut the pie in half. It would be my recommendation to postpone the trip, and save more money rather than thinking you could go and just pinch pennies.
If budget is not a worry, stay at the Napa River Inn. What an incredible location! You will have amazing dining, and even the Wine Train just steps from your hotel.
If you want to cut back, try the Best Western at the Vines. It’s still $200USD+ (weeknights)/ $300USD+ (weekends) it’s 10 minutes from the town and will require a rental car.
On the Napa River boardwalk, in town, you will find restaurants like Napa General Store and Celadon. $200 per couple would get you a lovely meal in a gorgeous setting.
If you want to cut back I would suggest going at happy hour between 4 and 6 PM. There are a few restaurants and pubs along that strip with $6 glasses of wine and $10 appetizers. We popped into Celadon and watched the mixologist at work. That’s right, not bartender, mixologist!
Napa Valley itself, is warm. In San Francisco and the bay area I wore long pants and a jacket and still shivered. Mere hours later in Napa,on the same day, I wore a sleeveless blouse and skirt and was very warm. The difference was “quite normal” said the locals and you can expect the Napa/Sonoma area up about 15°C warmer.
When it comes to paying for things in Napa/Sonoma area I would recommend cash or a credit card. Debit cards with chip or tap were effectively useless. Any of the counter machines I tried to use did not recognize a Royal Bank card. “Tap” is not a thing in this area. Ultimately I found an ATM and withdrew more cash.
In the USA when you say “debit” they think Visa-debit. Which is a completely different thing than our Interac system. Canadian cards are certainly not as useable as I thought they were.
Realistically, I think a couple could spend $400-$500 a day in the area, without even buying souvenirs.
If you would like more experiences, there are also two National Parks in the Napa area where you could go hiking and find waterfalls or even camp! Expect to pay entry fee to the park and of course, a fee for your camping site. If you want to see the Petrified Forest, (only about 20 minutes away) it is on private land and entry is $26 a person. There is also a gift shop.
The one thing I will say about Napa is the experience is as close to Italy as you can get without being in Italy. I think it would make the most amazing anniversary trip if you were celebrating 25 or 30 or 40 years together.