Cheap, good, popular and reliable - Lectric. $1000, 750 watt motor, 48 volt battery, fat 4" tires

I have the same specs in mine and it was $2300 and also now bankrupt (sondors fold XS)

If you want something more burly you can get a 52 volt bike with hub motors in both wheels, dual batteries that do 50+ MPH. Rad power bikes I think? Juiced, Ariel rider.. look in to those companies. Also super73 if you want it to look like an old dirt bike