I converted an old Ross to bar-end shifters. You will need shifters and bar-end pods, cables, housing. Rivendell, Velo-Orange and some bike shops sell the Dia-Compe ("Silver") friction shifters, Rivendell has the shifter pods. You can also use new Shimano bar-end shifters set in friction mode.

The really cheap way is with Sun-Race or Falcon thumb shifters on the handlebars. These are dirt cheap and very reliable, easiest set-up you will ever do. Rivendell and others have these. You get no style points for these but they are simple and they work.