If you REAQLLY want turbo, then there is no reason to start out with a non-turbo car. DO NOT waste the time or money. You will save a LOT on the build...insurance on a turbo car will be less over the long haul....
Or, you can buy the car in a 6 months or so, and do some of the mods you want... that way, but time you are 21, the insurance will have dropped.
My opinion is to NOT get the non-turbo just to save a few $$$ now, you will spend a LOT more in the long run..