I was thinking about how there are engine options for all the plane in Airline Mogul but no options to retrofit aircraft with blended winglets. The three main families that utilize these winglet retrofits are the 737 family, 757, and the 767 family. I have done a little research on these aircraft and their winglet options. This could be like and engine option and could be more useful in the future when runway lengths come into play.
737 Family:
-Offered on the -700, -800, -900 (standard on the BBJ)
-Up to 6% fuel savings on longer flights
-Less effective on shorter flights but reduce takeoff thrust which saves fuel and lowers engine maintenance
-Extends range:

-Winglets cost about $750,000 apiece with another $80,000 for installation for a total of $$1,580,000
-It takes about a week to install the winglets
757 Family:
- Offered on both variants
- Aviation Partners Inc. (maker of winglets) claims a 5% fuel savings and 200nm of extra range.
-Cost about a $1,250,000 apiece plus $100,000 for installation for a total of $2,600,000
767 Family:
-Offered on the -200 and -300 (-400 has raked wingtips like 777)
-”The 767-300ER can be retrofitted with blended winglets from Aviation Partners Boeing. These winglets are 11 ft (3.4 m) long and decrease fuel consumption an estimated 5%-6.5% on the -300ER”
-Hawaiian Airlines says 5% fuel reduction
Couldn’t find an exact cost so I extrapolated, winglets cost $1,750,000 with another $100,000 for installation
Sources:
-Wikipedia articles on each family
-Google
-
http://www.b737.org.uk/winglets.htm