I'm sorry but I don't know of any plastic surgeons in Louisville (or anywhere in Kentucky) so I won't be much help.
About the discount, how much did you have in mind? If the two of you do it together, that should be possible. Plastic surgery prices are just like anything else, they're always negotiable
Are the both of you average or under weight? The reason I ask is because it's always a good idea to be at your ideal weight before you get breast implants. Otherwise you may end up getting implants that that won't look right when you get to that magic number (of course if you two are happy with your weight, then this doesn't apply to you
I've never had the experience you're about to embark on, but getting plastic surgery with a best friend at the same time sounds like the way to go!