Under USD 100?
Unlikely, unless you have a serious stash of parts already.
Apart from the obvious - the bar - there are several other parts affected. Your brake/shifter combo won't fit on a drop bar. Your brakes won't work with the most commonly available road brake/shifter combos. Your front derailer might not play nice with a road shifter. A drop bar will put your hands 2-4" further forward. If the bike is correctly sized now, you'd need a shorter stem to compensate.
If all you want is a hunched down position for battling headwinds, consider some drop bar ends.
If you want multiple hand positions, consider trekking AKA butterfly bars.
Or maybe try scoring a split drop bar off a department store bike, which'd allow you to mount your current brakes/shifters by the flat center part.
There are drop bars in flat bar diameter - which would let you reuse your brakes/shifters, sort of - but they're kinda rare.
You might be better off spending that 100 USD on a used road bike.
