Omit price when zero (free)

If the price is zero, it would be much better if the line didn't show up on the various pages, such as registration. It is just confusing for free events.

I'd like to make it switchable - we have some events that we want posted (to save the date), but the details haven't been finalized. At the moment it says free if I don't put an amount in the price - I'd like a way for it to either say 'TBA' or be completely hidden for these events. But we do have some events that are free and I'd like it to keep showing the price for those.