As I’ve stated before it’s very hard to put a value on postcards. On e-Bay antique street scenes are getting fast and furious bids on street scenes ranging anywhere from $.99 cent’s to $50.-60.00 for one card. You need people from your area that collect these to drive the price up. If you want to sell them ,the best way is a local auction house putting a few up for bids over several wks. Go on e-bay and type in Antique street scene postcard and you’ll see what I mean. In my area local postcards go for alot and go very high at auctions for instance a flooded town went for $100.00 another one with baseball player,trains. antique cars etc. Where as yellowstone national Park sold with many more like that might only bring a few $$$$$. Average price for antique xmas or halloween, easter or valentines range from $10-15.00. Your question on vintage calendars are not as popular and usually are not worth as much. Again it depends what’s on the calendar.and condition.
my advice would be to buy a book on postcards (Amazon) or the library. Some postcards if they are street scenes from local town can go for $100.00 or more, Halloween, valentines, brewriess it just depends what’s on the card also if they have a stamp. there might be a postcard club on the web also. Have a good day!