Vinegar - there are entire sites devoted to its miriad of uses. I posted about some of its household uses last year -- but that didn't begin to cover everything that is great about basic, common vinegar ....
Medicinally, apple cidar vinegar is a folk remedy that garners thousands of testimonials, and has been used for centuries for everything from arthritis to depression.
Helping pets: from fleas to hot spots, vinegar has lots of testimonials to being a Godsend.
In gardening: spray it, undiluted, between the bricks on the patio to get rid of the weeds popping thru (yep, no more toxic stuff). I could go on and on and on.
Here's some sites to check out if you'd like to learn more:
And the cost? Amazon.com sells a huge bottle (128 oz.) of Heinz White Vinegar for $3.99.