You are literally the reason shelters exist. Ignorant people will buy animals knowing NOTHING about them and then give them off to shelters to take care of for their rest of their lives because they don't want it once it gets full grown.
Ready to be educated? Good. Reptiles don't grow to the size of their environment. Reptiles grow to the size that their food allows. If you feed them one rat a week, they will grow to the max size their body can sustain on one rat a week, which might be fairly large. If you feed two rats a week, that snake will be very large. Their is no max limit on how large they can grow because if they are given enough food, they will continue to grow. Now obviously, I doubt a corn snake will grow to be 10 feet long, but they can continue to grow throughout their life, albeit, slowly.
What python did you get? What breed? And this is honestly the dumbest decision for a first time snake owner...really. The best snake for a newbie would have been a corn or ball python because they don't grow that big and are probably two of the most docile snakes out there.
If the snake you got will get to be 10 feet long, the most economic decision would be for you to save up enough money to buy it outright. You'll need a custom made tank, so you can buy one online or something like that. http://monster-cages.com/cages.php has a lot of pretty standard caging for large snakes. But I'd also check your small pet stores (not Petco or Petsmart) because they usually get donated cages from people that they sell for cheap. Just get a large cage so that you won't need to continue buying one later.
Again, this was a not a smart thing to do for someone who literally knows nothing about the animal they're taking care of. For a snake that large, it will live for probably 15+ years. Just so you know.
Good luck