Try to find one used somewhere, like I did. You can get them MUCH cheaper than buying new. Or, find somebody local that owns one, and ask if he'd be willing to let you rent it. Even if you buy a new one and use it, you'll probably be able to resell it for a good price, if it's only been used once or twice.
Or, you can also buy one of these, and make extensions for the drill head out of iron pipe:
You can rig up a tripod and pully system, hang this one on it like the Deepwell unit, and it'll work just the same. Depending on how deep you drill, you'll need casing pipe, plus a water pump to pump in water as you're drilling, and you'll need to also use some sort of rigged up barrel inline with the water pump, to inject powered CLAY to keep the walls from collapsing as you drill.
Like I said, sledgehammer well is cheaper....
Ok, just for the heck of it, I checked e*bay, and found this:
Ok, looks like this forum censors links from a old established auction site. Just put e-b-a-y in place of the stars above, and remove the dashes first. Or use this link:
http://t-i-n-y-u-r-l.com/73nupg Put t-i-n-y-u-r-l without the dashes, in place of the *'s
I have NO financial interest whether you buy his unit or not, but it looks pretty cool to me.