Aaron, there are many different kinds of rehabs and qualities for each.
Perhaps more details of your focus could better assist us in answering your question.
For instance, are your rehabs for owner occupant flips, or for landlords? What materials are used in the competition homes in your area? (Knowing that will better help you answer your own question)
Buy carpet materials from a carpet wherehouse (not HD or Lowes). You can get most everything else at HD or Lowes. As others suggested, spend some time in HD/Lowes and price out materials which you will be needing (tile, laminate, paint, doors, windows, siding, landscape materials, baseboards/door casings, door hardware, electrical fixtures, bathroom vanities, closet doors, plumbing fixtures, etc.