Why do you want to buy a biocube, when they are so much more expensive and so much worse dimension-wise than a regular 29? I would not put any exodons in a 19" tank. Even a regular 29 is on the small side for them. But, I would just find a used tnak on craigslist, will be much cheaper.
On another note, at 14 you should be able to get a part time job of some sort. Earlier the bette! I started working at a mom and pop pet store when I was 14, freshman in high school. Funded my aquarium hobby for the next few years.