It depends on whether I am traveling solo in Europe or with the Mrs and family. That factor dictates the style and the style dictates the budget. I pay attention to the exchange rate Euro vs $ and how its effect on the cost of the trip.
Basically, I am a budget traveler, always flying non-stop in Economy (sardine can seat for ca 11 hours) to Frankfurt, Paris CDG or London, usually round-trip, but not always. No problem for me backtracking to London or Paris.
When I travel solo, obviously, I have far more options, such as staying in a hostels, not likely, but just depends on where as an option not to be precluded, taking night rains as I tailor the travel routes, using a rail pass, staying in 2 star hotel-Pensionen, non en suite rooms, choosing where to eat, either at the train station, picnicing in the hotel room at dinner, or restaurant with the occasional splurge,
Also choosing which sites to visit, the type of hotel to stay at. Staying in an apt or using Airbnb is not an option, regardless of how many nights in one place...two or 14 nights.
On transport costs....I take public transportation, all the different trains, subway, buses, Renting a car is not an option.
Since retirement I have been fortunate to make it back over every year, all in the summer, except once in April/May those two weeks. The minimum duration is 2 weeks, the max so far is 12 weeks, since retirement the max has been 9 weeks.
Ideally, I aim to do a trip, UK plus Schengen for a max of 100 days between May and early Sept.
On the daily expenses....In Austria and Germany I mainly pay in cash. That's the way it is done there, I oblige. In France, England, and other countries I use the credit card way more often but not exclusively...just depends where and how much is the purchase. In the late 1990s I used a credit card in Paris to pay for groceries at Monoprix and it went through, no problems.
I spend some money on souvenirs but not much...just depends where and what.