new engine bicycler

Hi all! I was a little overwhelmed trying to find a answer for a good starter motor so I decided to start my journey here. I have a 29" Mongoose Banish Mountain Bike I would like to use in my first build (A lot on ebay if you need to see it or check link below). This is a 21 Speed with...

I am looking to buy my first bicycle engine kit for my bicycle. I have been doing lots of research but I want to know what the best kit for $250 or under, including shipping is. I know I want a chain drive engine. Please help. Thank you.