There are a lot of cheaper ways to accomplish this goal. For less than the price of the parts, you should be able to find a complete road bike in ready to ride condition.

Switching a MTB from 26 inch wheels to 700c is a huge move. Are your cantilevers really going to adjust that far? Changing from a triple to a double is going to mean a new BB.

If you want to go the MTB route, why not just get 26 inch slicks and use it that way? That would cut a lot of the expense. Drops are a good idea, but to manage the cost, you might want to consider either barcons or DT shifters. If it was me, I would go with DT shifters.

As built, I have less than $75 into this Trek 950 MTB, including $25 into tires and tubes. Built this up from a cheap frame, plus a $5 donor bike.