Kaala, I in no way was trying to scold you, or your family or attack you personally at all, I was just pointing out some of MY concerns based on what you said. Your choice to handle it how you want. It is good that you are trying to urge your sister towards a more suitable beginner reptile. I also understand that you cannot control what she does with her money, but speaking to her can hopefully influence her and prevent her from making a poor decision. I think you should worry about building your cage before you worry about spending 100 or more dollars on an animal for your mother. You state money is tight, that sounds like that would not be a wise decision to make. You could probably build a custom enclosure for 100 dollars, and it sounds like from the skills your father has that should be quite easy for you to achieve.
Andrew