Hello and welcome to just answer. If it only smokes on start up, then it may be worn valve guides/seals. If it does not smoke while driving then it probably is not worn piston rings. Replacing valve guides is not cheap, but is cheaper than replacing piston rings. If it is just valve guides and valve seals, then figure on around $5000.00 parts and labor. If it is a ring issue, then budget for closer to $10,000.00 parts and labor. Whatever the case, make sure that it is diagnosed and repaired by a shop or the dealer that is fully trained and familiar with this engine. Don't let just any shop attempt this.
I hope this information helps, and let me know if you need further assistance with this.
Well signs of oil fouling on just one area of a spark plug's electrode insulator would indicate worn valve guides and/or seals, and oil if oil fouling is noticed all ove an insulator then that would point more towards a ring problem.