Buses and Trains and Renting Rooms
For the most part, we've been using Booking.com (similar to AirBNB) to find flats instead of staying in hotels. For the same or less money, we get a bit more space and a kitchen. In each city, we've been going grocery shopping and buying local foods (herring, pate, Estonia had amazingly wonderful tomatoes, fruit, cheese, oat milk in Sweden, etc.) and eating breakfast/brunch "at home" instead of eating out. That probably saves us $25 each day, plus we're likely getting a healthier, more nutritious breakfast.
The flats have - for the most part - been acceptable and clean. They each seem to have their little issues: in Latvia we have no microwave and we're a bit further from the center of towel (and, oh, the towels are scratchy); in Sweden the first two days we had no hot water in the shower so we had to use the sink (but we were in walking distance to the center of town and the flat was quite a bit cheaper than the VERY expensive hotels); in Kuressaare in Estonia the TV channels were really bad (actually that's been true nearly everywhere!). Plus, by staying in our own flat, we've been able to do laundry occasionally which has also been helpful. In any case, we've found this to be a great way to affordably and comfortably travel.
We also have figured out/learned that if you're traveling by train or tram in this part of the world, the tickets are sold in convenience stores. In Sweden we bought the subway tickets in a small convenience store right next to the underground gates (the woman at the ticket counter told us to buy them in the store instead of from her because they cost less) and in Latvia we bought them in a convenience store (like a 7-11) called Narvesen.
If you ever travel here, these tips will help!