Heh, money is a bad question on these.  To make the 400's 450's and 700's get up there in HP, it takes A LOT of invested cash.  I can only give numbers from my own experience with my 450....

Big 3
$250 - Intake Kit
$270 - Fuel Injection Computer
$570 - Exhaust

Big 4
$325 - Cams

More
$150 - Throttle Body Mods
$800 - Valves, springs, grinding, porting
$500 - Crank balanced & mods
$250 - Piston & mods
$180 - Rod

Ball park for this build is around $3500.  Of course the 400 above has quite a bit MORE custom parts and with that is quite a bit more money.  Figure some of the hill shooter 700's out there have $15k in aftermarket goodies!

And yes, these motors are so pushed to the edge of limits that they won't last long!
This is just cost on parts and some labor.  You have to factor in gaskets, builder costs (if you use one), etc....