I can't verify the validity of this but Wikipedia says that Spinning Dragons (for an example of a Gerstlauer Spinning Coaster) was just about $4 million. Steel Dragon at Waldameer is a Maurer spinning coaster and that also cost $4 million.
Even if these dollar totals are correct here is a problem with that, both of these roller coasters were made in 2004 so I'm sure prices have changed since then
Once again using Wikipedia and this number could be wrong (can you tell I don't really trust Wikipedia) Gravity Group wooden roller coasters are much over $2 million
For Example...
$6,000,000 Ravine Flyer II
$6,500,000 Voyage
$6,000,000 Mine Blower
I found out that Six Flags Texas' Tony Hawk's Big Spin (now Pandemonium) roller coaster cost $6,500,000 and that was in 2008. That was four years after Spinning Dragons opened at Worlds of Fun. The prices of Gerstlauer spinning coasters has changed slightly within four years between 2004 and 2008.