Undergarments...where to buy?

I have NO idea where to buy an undergarment for my dress...does anyone have any suggestions?

I am not looking to have something custom made because that will be ridiculously expensive.

I need a one-peice halter/bodysuit....maybe even a one-peice that goes down to the thighs (like attached biker shorts..lol)

i think the girls were talking about blum's in patchogue? blum's