Magnesium is a key mineral, if you search the forums you will see several threads on it.
For me the key is preventing muscle cramps. It's very obvious if I don't take magnesium, I used to get muscle cramps all over my body, not just legs.
Magnesium in general is very cheap.
But it depends on which form you take. IMO people do make to much to do about bioavailability. MgO2 is cheap but not highly bioavailable. Most versions of Mg you need to take with food. I take 500 mg triple mag complex which is MgO2, Mg citrate and Mg aspartate in one pill, it was fairly cheap.
Then I also take Magtein, which is expensive, but it's the only form that crosses the blood brain barrier and is highly bio-available. I usually only take 1-2 even though it recommends 3 because I already take 500 mg of the complex.
If I have a hard cardio run, I sometime take a hot bath in epson salts (Mag sulfate) which does a lot to relieve short term muscle pain. Also cheap, and it is absorbed through your skin. I experimented with drinking epson salts, it works but is yucky and tends to not be very bio-available.
I also take Boron (6 mg) which seems work synergistically with magnesium and both tend to be deficient in the soil/diet.
