I did that with my old Trek road bike... as I get older and stiffer I found I seldom used the drops and thought straight/flat bars would be more comfortable.

I found my neck liked the more upright attitude, but my hands and arms were very uncomfortable. I NEVER had hand or arm pain riding on drop bars, but I sure did on straight bars, especially after an hour or so. Bar ends helped somewhat, but are an extra expense.

Trekking bars look interesting and I would encourage you to look into those.

So... think twice before you drop a lot of cash on the conversion. I would probably not do it if I had it to do over again.

But to answer your question... I bought some Shimano combo brake-lever/shifters on Amazon for ~$15, bars were $25ish at the LBS, and grips and bar-ends. It all adds up. My bike is 3x7 and the older Shimano MTB stuff works fine.

Hope this helps!