Money is tight. Supplements are expensive. Which are the very most important?

I really want to figure out and take, on a continual basis, the supplements that are best for me on a long-term basis. I know that things like Fish Oil, Co-Q-10, vitamins and calcium are important; but right there, those things together could cost $30 or $40 a month for one person. That's way too much in this tight budget time.

What are the very most important supplements a person should take, beyond a good multivitamin? And if you've found a great place (online or otherwise) to get (trusted) supplements for less, could you share your strategy? Thanks so much.