Being a former Cobra owner I might have an opinion on this
Ok first and foremost you need to look at 3 things in my opinion those are: Price, Speed, and Style. So let's look at each car.
03 Mach 1: Base MSRP $29,330 great style looks much better than the 03 Cobra IMO, and is faster than a GT, S281, or older stock Cobras. It is the cheapest of all the cars mentioned and in my opinion the best bang for your buck.
03/04 Cobra Coupe: Base MSRP 34,XXX some dealerships mark these over MSRP as well

style isn't as eye catching as the Mach 1. IMO the car sports only small style differences over the GT (different hood, rims, bumper, badges, front fascia, etc. etc.) most of these are unnoticeable from a distance as well. The 03/04 Cobra is supercharaged with a very underrated 390 hp at the flywheel and is probably the best buy if you are looking for a car based on speed alone and this includes non Mustangs there is no car that sports this type of hp and 1/4 mile times stock for this price.
Saleen: Basically 2 to choose from unless you buy used the S281 or the S281-E now obviously the Saleens have better style stock IMO than any stock Mustang direct from Ford or SVT. They are definitely head turners and you don't see alot of them around either. Now here comes the problems first off let's just look at the S281 coupe you have a car that looks awesome but only comes with 285 hp at the flywheel stock and is only good for a 14.1 in the 1/4 mile stock (from
www.saleen.com don't debate it

). So basically you have a car that is slightly faster than a Mustang GT that looks really good but is slower than both the Mach 1 and the Cobra, and how much are you gonna have to pay for this? $34,194.00 base MSRP so for STYLE alone you are gonna have to pay as much as you would for a Cobra at least. Now let's look at the S281-E coupe once again you have a car that looks awesome but this one is supercharged and has 425 hp at the flywheel stock sounds like the best yet right SPEED & STYLE! Unfortunately here is the car's biggest problem IMO $60,190.00 Base MSRP

So here's the question you gotta ask yourself if you are thinking about a S281-E are you rich?
Roush: Is alot like Saleen (though IMO Saleens look better) they provide better style over the stock Ford Mustangs and some have more HP and are faster but their prices leave something to be desired from the average buyers point of view. Basically it's like this you take a regular base Mustang GT (with the exception of the Stage 1) then Roush goes to work on it for a price. When you get the finished product you are gonna have a car with great STYLE and SPEED but you are gonna pay the bucks. Let's look at price of a base model V6 Coupe & base model GT first though V6 - $18,345 GT - $24,330 now that we know our starting points let's look at each car Roush has made available and their price
Roush Stage 1: Requires a base V-6 or GT + $6,569.00 for a total of either $24,914 or $30,899 neither are supercharged.
Roush Stage 2: Requires a base GT + $9,860.00 for a total of $34,190. So now you have a nice looking car that probably outperforms the Mach 1 but is nonsupercharged and still slower than the Cobra but cost about the same lol.
Roush Stage 3: Requires a base GT + a minimum of $17,645.00 for a minimum total of $41,975. I say a minimum because there are 3 Roush stage 3 packages and this is the cheapest one lol "the sport". This Roush is supercharged and while the website doesn't give specifics performance wise I'm sure it can hold it's own with the 03/04 Cobra but I have my doubts if it's as fast as the S281-E stock vs. stock.
380R: Requires a base GT + $16,800.00 for a total of $41,130 (though I have seen them sold complete for under 40k). If I'm not mistaken (and someone will correct me if I'm wrong lol) the 380R is supercharged and the 380 stands for 380hp at the flywheel. Basically this is a alternative to the 03/04 Cobra, Stage 3, or S281-E but I've heard it's still slower than the Cobra.
Roush also offers other packages like Mustang Sport, Classic Mustang, and the Boyd Coddington Roadster but they range in price from $3,875.00 to $18,525.00 + your Base MSRP.
Overall lots of choices to choose from when it comes to Mustangs, personally with my budget I would go with the Mach 1 because it has STYLE and moderate speed even though I could afford the Cobra the Mach 1 just looks better and to me speed isn't everything. The high end Saleens & Roushes are great BUT and no insult to any Mustang owners here but if I'm gonna spend anywhere from $41,130 to $60,190 I'm gonna buy a Corvette, Porsche, Mercedes Benz, or BMW but that's just me.
