The fees for Cosmetic Surgery are always paid in advance. There are many payment options available: cash, check, credit card, loans from different sources like banks, friends, family or special loan companies. Your surgeon will assist in obtaining a reasonable payment plan.
There are multiple ways to pay for cosmetic surgery. Unfortunately, due to the economic situation many medical finance company either went out of business or changed their terms making them unattractive to both surgeons and patient. Rather than asking what the lowest rate is, I would advise you to see several Plastic surgeons and then ask the one you like best what financing options do they offer.
Plastic surgeons often use loan companies to help their patients, there are multiple companies out there - it is your job to reasearch what is available. Also try your bank or check with your credit card.