I owned an expedited freight/trucking company for several years, and your absolute last option should be going though a mega carrier's school. Besides being stuck working for them for a year if you fail the class or they kick you out for any reason (and you'd be surprised some of the reasons they'll kick you out), then you'll be stuck paying the entire cost of the school. Not to mention that you are at their mercy and will get the shittiest of the shitty loads and routes. Think the northeast in the winter running icy back roads because the company doesn't want to pay for toll roads (all the mega carriers do this and it's a huge cause of first year accidents and people getting frustrated and quitting), and known problem shippers that will have you sitting in their docks for hours until they decide to load you, all while your ELD is running and cutting your day short.
The other problem with mega carrier schools is you will be getting very little individual instruction time. They usually have one instructor per 5-10 people, and you will be in the truck driving with the instructor in the passenger seat while other students are sitting in the sleeper waiting their turn. So if you can't pick up shifting or straight line backing right away you are shit out of luck, it's an assembly line and they treat it as such.
It sounds like you are in a difficult financial situation, so you should have no problem getting approved for a grant by the state to pay for your school. And I wouldn't recommend Roadmaster either, as they are also a bit of an assembly line school. When I got drivers out of there they were never trained properly. If you are in Tampa go to Sage Truck Driving School
Tampa Truck Driving School – Florida CDL Training at SAGE – Sage Truck Driving Schools out of Hillsborough Community College Plant City campus. They are the best of the best in terms of schools, and it will always be one instructor per student. So all of your instruction would be individualized and they will work with you until you get it right. The drivers I got out of there were trained professionally and knew their shit.
The last piece of advice I can give you is don't settle for working for a mega carrier your first year. With the new ELD mandate the trucker shortage is getting even worse, as many longtime veteran drivers quit because they couldn't make the money they used to make when they could cheat their logs. The old rule that you had to work your first year for a shit carrier is just that, an old, outdated rule. If you see a good company asks for a year experience apply anyways, and you'd be surprised how many will waive that. If you can pass a background check get your tanker and Hazmat and stick with tanker trucks, there is way more money there than there is in bumping docks and running freight...