Aw comon, don't discourage this kid's creativity. Since when is it fun to just buy a part when you can make it yourself?
Making a mold and filling the mold is just to clone a part you already have. Unless the 'small orange dealie' you have is exactly the same as the one you are missing, making a mold isn't the best option.
You could always travel to homedepot / lowes and browse their aisles looking for some parts that you could improvise with or just get some ideas. Some common materials that are easy to work with for nerf guns are wood, pvc, and thin sheet metal, which are all cheap and sold at most hardware stores.
Hot glue is very strong as a single part when it dries, but it is very hard to release it from the mold you use, because it is a glue... it's supposed to stick to things it touches. I've filled a section of PVC with hotglue in hopes of making a solid hotglue cylinder, but after it dried i couldn't get the hotglue cylinder out of the pvc, it was stuck. So it probably won't work for making a part.
I heard these were high maintenance cars. My friend who owns a Rx7 says that the 3 tips of the rotor or whatever its called, the main part of a rotary engine, well anyway, the tips of that wear out quick. He is always fixing his car and I think rotary engines are just too much trouble for a first time driver.
But if you do get a sports car, opt for a manual (cheaper too). I learned on an auto, and now that I know how to drive a manual, I really wish my parents put me on a manual first. Also, having an auto sports car is just so boring. I have an auto 'stang and it is very boring to drive and shifts at the worst times (for economy).
They came out with this new tranny, called a tip tonic or some stupid name like that, but the idea is cool. Its a manual when you want it to be, and an automatic when you want it to be. My buddy recently bought a Nissan 350Z, and the tiptonic was actually the cheapest transmission, even though he gets the best of both worlds.