Interior French Doors

It depends on how nice you want them. You can get really inexpensive wood ones from Home Depot or Lowes. They are pretty lightweight, not at all like an original door would have been in your apartment but if your pockets aren't deep you can get a couple for as little as $125 or so. They come in a plain wood finish and you can stain or paint as you like. For nicer doors you can try Dykes Lumber or any of the specialty window and door stores. Or try a salvage place for doors to match the rest of your home.

Check Brownstoner.com for additional advice.