It's hard to say what is really a fair price jump, since most cars with turbos also add other additional equipment too.
For instance, we do have some idea what the Solstice GXP will cost. Bob Lutz has stated that the price increase will be between $4000 to $5000 for the GXP Solstice over the base car. However, we also know that this price increase includes about $3000 worth of non-turbo equipment, that is extra cost on the Solstice (things like ABS, convenience pkg, upgraded wheels, etc). If they hold to Lutz's statement, that would mean the real price increase for the turbo on the GXP would be about $2000, plus the rest of the equipment. That is also not counting the revised fascias, the stability control/active handline, or revised suspension on the GXP.
A $2000 increase could be reasonable.