A recent post in the "NICE! AWOL TrimTag?" thread brought to mind my vote for the most overpriced option in '68.

Option 731, Air Cleaner- Heavy Duty aka Air Cleaner - Dual Stage, cost $9.48 ($52.45 in 2005 dollars.) To the best of my knowledge, it consisted of adding a piece of sponge-like foam around the paper filter element and putting a different lable on the aircleaner housing. GM may have also sprayed a little oil on it. The last time I purchased a new AC A279C filter it came with both the paper and foam and cost $6.11.

I think GM's margins were pretty good on this option.

No post by me would be complete w/o a picture: