If you are looking at a '99, make sure that the recall has been performed (this was a MAJOR black eye for SVT)
If you want to go fast for cheap, look into an LS1 F-body (Camaro or Firebird).
It will eat the lunch of the Cobra plus it can be had with the beefy T-56 6 speed manual, the same trans in the Dodge Viper.
If you want to spend a little more, say 20k, you can get an LS1 or LS6 in a GTO with the same 6 speed.
All the above cars are very fast with some F-bodies running high 12's with VERY minimal mods.
The only drawback is that the car surrounding the wonderful LS1 is a POS.
No fewer than 5 times I have decided that I am going to get an Fbody due to the performance. Every single time I walked away thinking what a terrible car. How can one vehicle have so many flaws in ergonomics and execution? HUGE outside yet cramped inside and more squeaks and rattles than a Day Care center.
I'd still take it over a Neon SRT4 though.
Good Luck!