What helps nails get stronger?

My nails actually crack in layers sometimes at the edges (into two layers, like, top and bottom) and I don't know what it is but a tiny layer also peeled, so on top my nails instead of being smooth, it's actually a little bump and ridge-ey (?) But um, is there a vitamin thing I can put on my nails or anything? And where can I get it? Also, I'm one of those people that buy only the lowest price items, so....