Question

Cheap is to valuable as common is to?

Answer 1

Rare, I believe.
Because the opposite of cheap is valuable, so the opposite of common is rare.

Answer 2

Cheap is to valuable as common is to:
- rare
- irregular
- unique
- uncommon
-unusual
- peculiar
- abnormal
- strange
- unusual
- individual
- separate
- unpopular
- exclusive

I hope this helps you! :))