I would talk to a nearby teacher, probably at your local high school, and see whether you can work a deal for lessons, advice and maybe try both trumpet and sax. As another sax player, I'd comment that there is more opportunity to play popular music with small groups (rock, country, etc -there are even a few celtic bands that use a sax) with the sax. If you decide to go with a sax, you want a tenor rather than an alto - the sound seems to work better with most popular music, and you will be playing in slightly less extreme keys - one less sharp than an alto or baritone.
Side benefit: If you like celtic, pennywhistles have the same fingering as the sax.
You'll also find that most bands with guitars and singers will be playing in keys with several sharps, so concentrate on becoming comfortable in those keys. Most popular band musicians (at the local level) don't read music, you'll be one of the few that do. It's not really tough. There is a guy in our local community concert band (actually a very good band) who plays tenor next to me who is completely self-taught. While he's not a top-level musician, he gets by pretty well, and we play pretty complex music - so you CAN DO IT.
Play lots of long tones to learn to have a good sound and stay in tune, play along with recorded music a little every day to get use to "playing by ear", and make up tunes some each day - people who learn to play by traditional methods get the idea that improvising is a magic process, complete with secret handshakes, where in reality it is the most natural thing in the world. If you can whistle an original blues riff, you can learn to improvise.
I real somewhere that the most effective way to practise is not to kill yourself for a couple of hours once a week, but to practise for 15 - 20 minutes every day, maybe twice if you are really into it.
Charlie Parker once said, "first you learn the music, then you learn the horn, then you forget all that and just play." This takes a while, and you never stop learning.
Best of luck!
Good luck - making music on any level is very fulfilling.