Engine Lifter Repair - 1997 Isuzu Rodeo

Hello, I have a 1997 Isuzu Rodeo, v6 with 145500 miles on it, I am use to the "Lifter Noise" and try to keep up on the oil changes. My mechanic began adding Lucas oil additive with my oil changes and the noise quited a little, the "problem" I have is for the second time now this lifter issue has caused my CHECK ENGINE light to come on while driving on the freeway.
my mechanic hooked it up to the code reader and it says that the #6 piston has misfired or something along those lines. The first time this happened my mechanic thought it was do to a low oil level so we changed to oil and added the lucas as well, today while driving to work the light came on again. My mechanic checked to oil level and said it was fine, not do for an oil change for another 1000 miles. He then suggested I may need my lifters replaced to stop the misfire from continuing to happen. My question is, how much would this repair be? And would the "lifter issue" real cause the #6 piston to send a misfire code? Thanks for any help with this problem.