Advice on a getting a new mustang

[PaulL]

Hi,
I'm thinking of getting a used mustang ... I like the body style of the new ones (99+), and I want a fast, powerful one with stick shift.
I was thinking of a used Cobra or maybe Roush, but had these questions;

I heard the Cobras under-performed in '99, and they didn't even make them in 2000. Does that mean I should only look at 2001 or newer?
How much did they under perform in 99? Maybe it's no big deal.
Can a GT be made as fast as a Cobra pretty cheaply?
The Cobras had special interiors, didn't they?
The Roush packages seem pricey ... I bet I could 'make my own Roush' for less money.

I'm hopin' to find something for under $20k. I know that'll be hard to do if I need to stay with 2001 or newer. But if a 99 Cobra is still similar to the 2001, then maybe that's the way I'll go.

Advice please?
Anything special to look for?