Nick-
It appears from the nature of your posts that you haven't had a hard dose of reality yet. It's crazy that you've even considering a car like a Mercedes or Mustang at 16 years old. Yeah, we all sat around and drooled at them in car magazines, but in real life things are different.
Considering your age and location, you are looking at paying at least $2000 a year for car insurance on a beat up ghetto sled, let alone either of the cars mentioned above. Insurance prices go up almost exponentially as the value of the car increases. The hard truth is, as others have mentioned, is until you turn 25 you are going to pay a lot for insurance, and even more if you crash or get tickets.
If you have the money to buy a car, get a decent used car with low miles and good mechanical condition. If you have money left over, stick it in the bank for future car repairs/mods. Don't blow your $$ wad on a "tight" ride just because it looks cool or goes fast. Save that for after college and you have a nice career.
Personally, I'd look for a nice used midsize sedan that is a few years old and gets good gas mileage. Contact your insurance company before you commit to any one car, and find out how much the insurance will be before signing on the dotted line. Remember that things like ABS, airbags, factory security systems and aftermarket security add-ons like VIN etching will reduce your insurance premium.
Having turned 26 this year, I can happily announce that my insurance fell like a brick on my two cars, even though one of them is a 4 door gas-guzzling hotrod RWD sedan. However, it was also only just this year that I bought my fast car since the insurance would have killed me, even with a very decent job and no tickets.
When I bought a new "family sedan" 2002 Impala LS back in '01, my insurance went up quite a bit....I also decided after this experience it's damn near useless to buy a brand new car these days, but that's besides the point of this thread.
Point is, save your cash and flash for later in life and buy a decent car now that you don't mind core-punching with and gets good gas mileage that you can afford to insure.