Here is a funny thing I learned. I went and got a 2.5 gallon tank for a Betta tank. I thought that it would not cost that much being it's only a 2.5 gallon tank. I ended up spending a little more than 100 dollars.
Decorations, a heater, a little filter, and also a light. Didn't think it would cost much. I am sure that I didn't need a lot of what I bought.
My point is just because your 13 does not mean you can't get a bigger tank, or take on a fish that's a little harder than most. Also the tank itself is not much usually it's all the other stuff you need that raises the cost. Does it come with a heater? Does it come with rocks and so on? You sound like a very smart kid when it comes to fish tanks. Just don't forget to cycle the tank first, before adding fish!!! You can look up all the information you need. Most of the time it's just throwing a uncooked shrimp into the tank and letting the Bactria grow. It's a little more involved than that, but that's the jest.
I think you can do the puffer if you really want too, it may cost a little more for the food, but it's not that much more. I think you should go with what you really want, because once you get a tank going, it's there for however long the fish live for. So get something you know you like, and do the research on the fish you want before you make the purchase. Researching the fish you want and finding out what it needs in order to live a full life will save you A LOT of time and money!
Here is a pic of the betta tank that set me back 100.