We could add in other cities as well. I have read that Budapest is fabulous that time of year.
You heard correctly, but I am a bit biased.
First, you say this year or 2026 or 2027. If funds are a bit tight for this year, you might find that Budapest is somewhat less expensive than Paris or a lot of Western Europe for that matter; so, it can help balance the cost of a holiday or it can just be the holiday. Budapest winters are a bit warmer than Paris as well.
Paris to Budapest: Booked today for 8 December on Wizzair with a checked bag is right at $100.
Seattle Round trip to Budapest: Mid December for a week, starts at about $1200 for one level up from Basic Economy.
Hotels: I just checked some hotel prices for another Christmas visitor and there is a perfectly located, no compromise, 3-Star for about $100 a night and a handful of equally as well located 4-Star hotels for under $200 a night (like this one: https://youtu.be/_kusvljyDN0?si=5EZ9-1nRUN6a9o48). Those prices with equally convenient locations and quality might be difficult to replicate in Paris.
Local Transportation: You guys, over 65, get to travel all the public transportation, even the trains within the country for FREE. No cards, no tickets, just get on and ride. If you don’t mind the bus (it’s nice actually) even getting from the airport to the city center is free for you.
You need 3 full days to do it justice. So that is not less than 4 nights. But I have friends and know of a few Rick Steves forum members that come to Budapest every year for a week or more each trip and are still finding more to see and do so as a stand-alone trip 7 nights isn’t crazy. You just do a few day trip and slow down a bit. Here is a decent place to slow down a bit: https://www.youtube.com/shorts/tJ7TvLF0ZZA
The vibe at Christmas: https://youtube.com/shorts/PCgmLIw3PqY?si=eMSCWafbgm90Dx7G AND https://youtube.com/shorts/GTwhR6swMMs?si=P_SPi2LZaP5I8Mcr
The day trip I would do would be Szentendre. It’s a 45-minute commuter train up the river. Lovely town and lovely market. Again, it’s a free trip for you (over 65). Given time there are other ideas like Eger or the Archabbey at Pannonhalma; maybe for a Christmas concert.
If you want to pair Budapest with another place, look at Vienna. It’s 2:40 away by train for as little as $20 a ticket. Vienna does tend to have Paris like prices, but we have Emily on the forum who has been helpful in finding good accommodations in budget. Also, very nice markets. Emily has a post on the forum with information on the Vienna Markets.