どのくらい

どのくらい asks "how much" of anything you can measure: time, distance, amount, degree. It goes before the verb or adjective it asks about, before a noun with の, or at the end with ですか. どれくらい, どのぐらい and どれぐらい mean the same.

The answer usually takes くらい or ぐらい as well: "about".

どのくらい or いくら

For a price, ask いくら. どのくらい asks about size or amount, and with money it asks how much you will need or spend in total.

• × このかばんはどのくらいですか → このかばんはいくらですか