a web page or auction page

Mark Majka in Aurora ILL he will be able to fix you up.  630 499 5428

Check out the Equipment Exchange on this site.  (Personally, I don't like auctions.)

I want to save up my money and buy one for my 18th birthday, i want to know what a fair price is.

Is the must be 18 gun law more like 18 to rent R rated movies or the must be 18 to have sex. you know know big deal, or a fellony?

18 for long guns.  Serious crime, and any real dealer isn't going to talk to you (and should probably turn you in if you attempt to avoid the law).  

Any firearm you buy OUT OF STATE via a web page or auction site must, by federal law be shipped to a dealer in your state.  It cannot be shipped directly to you.  If you buy in state, you may be able to check you local/state laws and see if it is possible to get it under 18 by having a parent/guardian buy it for you legally.  

AFARR

Edited to add:  If you are looking to buy one for your birthday, you can probably approach a legitimate dealer just before your birthday, tell him you are going to get it shipped to him (he needs to send his FFL to the person shipping it) and ask him to hold it until your birthday.  He may even let you fondle it until then (but he cannot sell it to you until then).

Fair price for a New one (true NIB) would probably be $1500+ for a real unfired Colt.  Used at about $1300 in real nice condition gun.  Used with a little honest wear and tear would be $1200.