cheap hardy and easy plants can I use to make a real beautiful planted tank:
My suggestions would be: any anubias specie, java fern, bulbitis
Main problem I see is that silver dollars are notorious plant nippers/eaters. Most cichlids and plants don't go together (due to their tendency to rearrange decor). Most of the more peaceful cichlids don't mind valisneria (any specie), but they are soft leaved, and the silver dollars will probably tear them up. If you decide to do some plants, stick with cheap, and 1 or 2 of each specie, to test if the inhabitants decide to destroy...
As a side note, my oscar will only tolerate plants in one part of the tank, and shreds anything planted anywhere else.