Not much if you're not lightening your skin beyond it's natural shade.
LA 90% 40oz...I have been using it for peels and lotion. I have been using that same bottle for almost 6 months, and still have a lot left.
KS Soap.. I purchased 4 bars, and have have been using for almost 6 months. Have 2 bars left.
Nadinola..Purchased 3 Jars, using off and on for almost 6 months. Have 1 1/2 jars left
My most costly purchase $67. That was for Retin-A and HQ 4%. Got 6 tubes of each, but $25 of that $67 was for S&H.
I also purchase soaps locally which I will not do again because they are not as effective as KS.
Also purchased MSM and Vit-C powder which I use for Serum, general health, and hair.
All in all if your purchases have multi use it's not that expensive, and they will last for months.
Oh, and I did get Zinc Oxide for DIY sun protection. This depends on the frequency of use. I only use it on exposed areas when outdoors. The 2 packs I got may last more than 2 yrs !!!