I'm going to be straight with you because when I was 16 (oh the good ole days [8 months ago]), I started with a beater mustang and I fixed up the interior a bit and sunk probably 1700 or so before it was acceptable. That was of my own money, not to mention what my parents did to get it inspection ready.
Anyways. as far as each car goes this is what I have to say
Foxbodies:
79-86 more than likely not for you, unless you like four eyes (I do) and carburetokIHOERH:OIERH:EWOr engines
87-93 all great cars, I prefer the 87 to 89 for interior reasons, they all respond well to horse power upgrades because of non-strict emisson controls at the time. The down side to these cars is gas, if you plan on driving a lot, then don't bother with a 5.0, it'll burn a hole in your pocket fast(I have a 20 mile round trip going to school).
Sn95s:
94-95. There are 5.0s you can go with which make decent power and have nice styling cues, down side is that strict emissions, bad gas mileage, unresponsive engine ,lower selection of parts because of the different set up compared to foxbodys. I like my 95, but it's really a love hate relationship.
96-98 changed to the 4.6 still make as much power as before, modern engine, uses OBDII scanners now, plenty of parts ready to you.
99-04 not my cup of tea, I don't know much about these cars, but you can afford a few of the older ones.
I think your best options that I know about are 87 to 93, the risk is gas and that anything can be wrong with a 20 or so years old car. Or the 96 to 04 sn95s/new edges. Most 99 to 04s are better kept from what I've seen since they're not dated yet, and the sn95s just look better than the ned edges.
It really depends if you want a cool looking car, gas efficient or not, high performance and so on.