I had a set of SunTour Power shifters on a Nishiki way back when. I didn't like them at first but grew to like them, though had a pair of barcons been available to me I would have switched. At that time I had not yet ridden with barcons. Once I did, I forgot all about the stem shifters!

If you have downtube bosses already, DT shifters can be had on ebay for very little. It is your cheapest option, if that matters.