I can't be bothered going for four for the moment, though it's certainly plausible. So I stuck with six.
Basically all you really need is $16000 to completely upgrade your launcher.
That said, though, it's almost certainly as fatal as Verne's original idea :P Given that not counting air resistance, the hedgehog would have to be travelling at about 11km/s (28000mph) by the time it left the catapult. And that's one heck of an acceleration...probably somewhere in the order of 1000g...
