Here's a couple of true sub-$15 wines that I like:
Muscadet by Pepiere (Sevre et Maine Sur Lie, Gras Moutons, Briords) Luneau Papin is good also.
Cab Franc - Domaine Guion (Cuvee Domaine, Cuvee Prestige).
Cava - Raventos Reserva
Gamay - Terres Dorees aka JP Brun (Beaujolais Blanc, L'Ancien, Rose d'Folie (Sparkling)
Riesling - Donnhoff Estate Nahe (right at the edge as WS-Pro has a few places at 15 and change.)
Other - Gruet Brut Rose.