Brake pedal goes to floor

Price will vary greatly depending on what the actual problem is. Do you notice any loss of brake fluid onto the ground that would indicate a broken or leaking line? Does the pedal slowly go to the floor but you have brakes or does it drop fast and no brakes?
How long has it been since it had any brake work performed?
Did this happen fast or after a panic stop? Any grinding or other noises while stopping?

As to price, if it is something like a burst hose it could be under $100.00. If it is more serious, like failed calipers or master cylinder it could go over $800.00 to $1,000.00 very quickly depending on what needs to be done.