Do I have to give a price?

Yes, you need to give an indication of how much you charge.

Unless you used a "fixed price quote", it's not legally binding, and if you can't give an approximate price, use the dropdown to select a price range or hourly rate. Never give a price like $2 or $1,000,000 - you may think it says "I don't have enough info to quote" but to customers, it says "I can't be bothered to do a proper estimation on this job".