There have been a few threads on this subject over the last few months, generally, you need to workout if just buying a complete bike is a more cost effective option.

You would need a new stem, bar, shifter, brake levers & grips at a minimum. The design of the frame plays a part, is your current road bike sporty or more endurance based, as converting an endurance design would be easier, as it is already more upright.

Would also be looking at the current condition of your bike and see if there is anything else needing replacement, and then do the math.