Hire a guide and go catch baby tarpon. If you hunt around on Google you'll find there are loads of guides in Miami, all of them supply the gear, some will even pick you up at your hotel and drop you off at the end of the day. It's not cheap, but you've got almost a year to squirrel away the Pesos ... put a few bucks aside every week and it's easy to save up enough.
A day of baby tarpon fishing is by far the best bang for the buck in south Florida. "Baby" tarpon generally run from 10 to 30 pounds, you get them in numbers close by the marinas (so no long, long rides out to the spots), and they fight like crazy. Imagine catching a whole bunch of adult chinooks by casting swim baits on a bass rod, big difference being the tarpon don't just run, they also jump like they've got a butt full of TNT.
Forget about going for big tarpon, it's too much work for a 13 year-old. Tell the guide you're more interested in numbers and they'll fix you right up. You'll also probably catch some bonus redfish and snook too, so it's a great experience that you and your lad will remember for the rest of your lives.