Round trip 2 countries. What is the best and cheapest way to cover?

Cheapest depend on your age and how willing you are to fix a booking long time advance and no changeable.

Best for this is likely the same-there are passes, on which this site is based, but you have again chosen the worst and hardest countires to travel in with pass. All trips need also reservations-a major stumbleblock.

Any general forum advises people like you to do fixed advance.

Note that this is not a roundtrip (we call that return here in EUR) and also that for some sectors, notably to Lisboa, the train service simply is not very good-if not quite bad. IF U are the tipical USAer unused to it all, fly.