A gas turbine light helicopter is on average at least 10 times as expensive to charter (wet hire) as a piston engined light single fixed wing.
Well.... what would you expect of such a comparision? A more appropriate comparison might be with an R22 - about $230 (U.S.) per hour (dual) in these parts. Last I looked a light piston single (C152) was in the $130 - $150 range per hour dual - not such a big difference. Bell 206 about $950 - $1100 per hour; single engine turboprop (Piper Meridian/Pilatus PC12) about $900 - $1450.