2003 Mustang GT Convertible?
I think the first poster was high maybe when he was typing. I think the 2nd post is closer to accurate, but the 0-60 will be probably closer to 6 seconds or worse. I would add about 80-120 lbs more for the convert. in the weight department.
As far as running 12s costing 50K is ridiculous and spoken like a true person that has never built a car before. I put my 99 GT Auto in the low 12s @ 115 mph with 5K. 3.73 gears, Transgo shift kit, Nitto Drag Radials, 2800 Stall converter and Vortech V2 S-trim. For about 20K, I had a fully built car from end to end, turbocharged, that ran high 10s/low 11s all day on pump gas and low boost.
The auto with the stock converter and extra weight doesn't help, but these things can be overcome quite easily. If you just put in a quality( Precision Industries Stallion) 2800-3000 stall converter. shift kit(or Jerry Mods) and 3.73 gears, you will not recognize the car after that. Those mods alone will knock off almost a full second in the 1/4 and make the car much more fun to drive. The stock stall is a killer, but necessary from the factory I guess.