A frugal beauty tip I found in this Wise Bread Forums topic:

1-2 times per week, put 1/4 to 1 cup of olive oil in your hair (depends on how much hair you have and how well-coated you want it). It feels very odd at first, as it soaks up whatever you give it (start slow and you can always add more). Wear a shirt that you can ruin, of course, and you’ll want a disposable shower cap OR I just use a ponytail and then 1-2 plastic grocery bags tied near the nape of my neck.

Leave on for at least 1/2 hour, and you’ll want to do this right before washing your hair. When you shower, shampoo and then use a regular conditioner.

I assume it doesn’t have to be pricey olive oil, or else that would defeat the whole frugal angle.