The biggest factor is whether you own your car or are still making payments.If your girlfriend does not want to spend so much money on a mustang make a compromise. A new GT is $24000 out the door. You can get a base Focus for $13000(for your daily driver) out the door and spend the rest on on 4-cyl Fox body $1000-$3000 and drop a V-8 in it.The $200 you are gonna save every month on insurance you can spend on her($20) and on aftermarket parts($180)LOL