Hi! I'm a beginner to making props too, but my friend, who does Industrial design has been helping me (well, as much as he can without doing it himself -.-).
I'm wanting to make big staffs too ^^; but its really complicated T_T
This is what he e-mailed me concerning a small dragon prop I was trying out ^^;;
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The cheap way is to sculpt it out of urethane foam, and coat it with spray putty. You might get slightly less detail and it might need to be a little oversize, but it will be much cheaper ($20 or $30) and still look very good. The best thing for the handle would be yellow, blue or grey type urethane foam which is what we use in ID. You start with a block and sculpt it by cutting and sanding, and it stays pretty strong. Problem is I have no idea where you'd get it... (sorry!)
The fun way involves an air-drying modelling clay called "DAS". It takes a LOT of practice to get used to but it's fun!
The ghetto way is to sculpt it out of aluminium foil! You could then skim coat it with real putty or filler. This costs basically nothing and is very quick and easy to do, so you can do lots of practice runs!
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From what I've tried so far (not much lol) DAS is great but its pretty delicate if you're doing very finely detailed things, and (sorry if this sounds stupid, I didnt realise this was the case) if you do it solid then its likely to crack.
Anyway, these are just what he reccomended to me x.x; So I'm not sure how they work in detail. And, I've only had a chance to try out DAS... so if you find anything that works out well please tell me too!