I prefer to start at the beginning and learn from being efficient rather than spending money on parts that is very wasteful.
if i dont do any of the following :
break something i needed for a project
drive fruitlessly all over town for something i need for a project
hurt myself on a project
spend all day sanding/bondoing/wiring/etc and have to redo it
then it isnt a project. these are things i expect to encounter when im working on something, and deal with it on a weekly basis.
you cant expect to ask "what should i do for my first prop" and expect it to be the most beautiful easiest peice of work you ever did. if you want that, they sell model kits at micheals, go to town. when you're ready to make a prop, you learn efficiency as you go, and also learn the ropes.
you'll also get bondo and various other unclean things under your fingernails. if thats a problem, model kits are at micheals.
i just recently purchased an electrical clamp i needed for my army of darkness chainsaw, it was 2 inches to big, and i cant return it. thats 20 dollars i need very much thrown away.