Duolingo - You're not just learning a language but a life lesson lol

not as a set expression, but if you want to say that there are no things both cheap and good, than yes, natives would say it. Although, I think "Albo dobry albo tani" is more common. (At least where I live)

I'd say the second 'either'.

The second ‘either’ doesn't appear in English. (Actually, it sort of does: as the ‘or'. A thousand years ago, ‘either’ and ‘or’ were the same word, ‘othe’.)

No. This is a set expression and only using two times 'albo' makes sense. The thing about 'albo' is that it technically is "exclusive or" (even if people don't really care about it), and as this phrase is intended to be exclusive, only this works.