Aye, there are a lot of varying factors that go into cost. I couldn't say how much I think that'd cost, but I can say, as a general rule, giving yourself LOTS of time before the con to work on it will reduce cost. Trying to find your missing piece(s) a couple weeks beforehand or rushing into your pricey materials without testing on something cheap when you're unsure will only make it more expensive.
On any project, you'll almost always end up with one of the following situations:
1: Get it done cheap and good quality, it'll take a long time.
2: Get it done fast and good quality, it'll be expensive.
3: Get it done cheap and fast, quality suffers.
ditch - a safe place in an unsafe world