"You can buy all the filters you want, but when the stuff dissolves in the water, you can't get it out with media filters."
Not true, at least for most of "the stuff dissolved in water", which refers to dissolved salts, and organics. There are multiple media types which can remove just about anything either by ion exchange, oxidation, reduction or absorption of a combination of the mentioned. Agree with Firebrick43, RO is over-hyped, and for human physiology, is not good without adding
back vital salt nutrients (nor does it taste good without those salts). As Firebrick43 points out it is not "pretty cheap" (unless you live in an arid region).