We found a low-cost, do-it-yourself competitor with WD-40 lubricating spray: Vegetable oil and acetone
A team at Drexel University in Philly conducted side-by-side comparison tests of vegetable oil mixtures, WD-40 and automatic transmission fluid, and found that a mixture of vegetable oil with 10 percent acetone works as well to free rusted bolts as WD-40. And it costs about one-tenth of the price. Add more acetone, up to 30 percent, and the mixture works even better than WD-40 and still costs about one quarter the price.
Acetone, by the way is the active ingredient in nail polish remover and some paint thinners, and DIY mixtures with transmission fluid are sometimes used as a penetrating oil.
[Images by (left to right) cottonseedoil, dchou0123 and ATWJ - mhoey.eu / Flickr]