It looks like you're on the fringe of both the Sprint and Verizon Orlando EV-DO clouds, so you might be able to get high-speed Internet from either of those. It looks like you have OK T-Mobile EDGE coverage, too.
So it's just down to price (and double checking that coverage with stores and friends in your neighborhood).
Sprint has the best bang for the buck: $40/month if you also want a voice plan, $50/month without a voice plan, to tether a phone via USB cable to your Mac for unlimited high-speed access. I've regularly gotten speeds over 600 kbits/sec, up to 1 Mbit/sec, on their network. The Samsung MM-A920 looks like the cheapest phone you can do this with.
Verizon will let you tether a phone like the admirable Motorola E815 for $60/month, at pretty much the same speeds as Sprint.
T-Mobile will only charge you $30/month to tether with a whole bunch of their phones, but EDGE is a lot slower than EVDO ... think 100-150 kbits/sec, or about double the speed of dialup. On the other hand, you also get unlimited Wi-Fi at Starbucks for that.
Tethering EV-DO via Bluetooth (as opposed to USB) is not advised, because Bluetooth is slower than EV-DO ... so the Bluetooth becomes a bottleneck slowing down your connection! Go with a USB cable, you get a higher quality experience.
Read my stuff on pcmag.com for more - just search the site for EV-DO.