If the bike is excluded out of the cost, then you couldn't go wrong building a faring. Your range per cost ratio regarding your battery pack, as well as your top speed per dollar spent on ev parts, will improve dramatically, provided your route is anywhere from moderately hilly to flat(steep mountains would be an issue that negates much of the advantages of the faring).
Type in "bicycle faring" in some image searches and find some ideas.
There exist many 3/4 wheeled velomobiles and 2-wheeled streamliners where you only need 1 kW to do over 50 mph whereas an unfared competition road bike on flat ground with no wind would struggle to do 35 mph on 1 kW electric assist plus vigorous pedaling from the rider of 300W or more, and a DH/mountain bike would struggle to exceed 30 mph on that same 1 kW.
$1,000 could get you more than a reliable kW to play with, if you pick your parts wisely. Overvolting a cheap kit and using a modded Infineon controller by Lyen with cheap hobby king Li Poly is one way to get that on the cheap, but far from your only option depending on what you're willing to compromise.
Safely doing 50 mph, without significant expense on modifications to the bike chassis, could be an issue. $1,000 may not get you a lot in regard to that unless you can do custom work!
If you want to keep it simple, 30-35 mph would be all that you can reasonably expect for that $1,000, but you need not limit yourself to that if you're willing to put in the work.
