What do you mean by 'kid's'? - Are you talking to fit someone 4' or 5'? (5' you could put them on a small-frame adult bike - 47-48cm)
How good are you at bike maintenance / building? - cheapest is always used if you can spot problems and fix minor things - and tell the difference between major and minor things
What do you mean by road bike, for that matter? Is Jr. going to be racing, just looking for drop bars, or are you even looking for a drop bar bike?
The
Soma Bart/Lisa frameset is I think the only one I know of for 20" wheels, most of the kids road bikes are for 24" or 650C.
Norco Valence 24" MSRP is $570 USD / $750 CAD
It's also quite possible to add drop bars, narrower, near-slick tires to just about any bike using short reach levers (linear pull are available) and a bar end shifter.