[DoctorDomo]

Epsom salts are dirt cheap. Citric acid isn't too expensive. Magnesium citrate capsules are a complete ripoff. Citric acid + MgOH would be the way to go, but milk of magnesia is expensive. Since its a chelator, the citrate ion should dominate the equilibrium. I reckon glycerol would be a good solvent since there'll be a lot of hydrogen bonding going on there. Not to mention you get this kinda thing going on:

they call that magnesium citrate 3:2, and its much less soluble in water, so with the right volume of aqueous solvent, it might crash out easily.

[Intanjir]

As is often the case with supplements you can buy the powder like 5x cheaper than the capsules.
Edit: Nope I am wrong. Citrate is rather heavy and the powder people include the citrate weight and capsule people don't.