There are three Generations, and not four.
You can see the 'breaks' in the Colt Serial Number' thread I posted here.
The newest-built Colts are excellent examples, but Colt's production is very low, so if you want a brand-new one, your best bet will be Gunbroker, rather than placing an order with the Custom Shop or waiting for one to appear on a dealer's shelf.
There have been a lot of discussion on this forum - read it - you'll learn a lot of interesting things, all of which will help you as you search.
The lowest cost to you will happen at a larger show - on a Sunday - for straight cash - from a dealer who'd like to go home with actual money in his pocket.
Decide on a caliber and finish, as well as barrel length, then you can limit your search, but if you'd like something unique, then look for the re-issued .44-40 with the blackpowder frame and etched panel on the barrel made just like the early ones were 'back in the day'.
Good Hunting!
Scouts Out!