Pistons are only the tip of the iceberg. You crack open the block and you're looking at replacing a lot of gaskets (head, oil pan, etc.) and bearings (rod, main, thrust washers, etc.). Depending on which piston, you may need to have the stock rods machined so the wrist pins fit. Aftermarket rods can be used, but at extra cost. Depending on the condition of the cylinder walls, you may need to have the walls honed or even bored out (in which case an over size piston would need to be used).

IMO putting a turbo on a non-forced induction car takes some time, planning, and money to do it right. There's more knowledgeable turbo guys on the board, so hopefully they'll chime in here.