Only for a few days, essentially working from CZ over through to AT (Linz>Salzburg>Innsbruck) and then into CH from there.

That's a lot more expensive than I was expecting!

For CZ, nearly every govt page and article I have found just says that foreigners from orange/red countries need a test to enter, but one page only, says that foreigners from orange/red countries still are not allowed entry for tourism purposes, even if they have a test (here). I've emailed the govt to try to get clarification.