What is the cheapest beginner motorcycle for a 23 year old 5'7" 140lbs guy who has never ridden before.

Honda makes a Shadow 600 and 750, both of which are good starters. I have a Honda Rebel 250, and it's a fantastic beginner, but you will want something bigger in a month. Yamaha V-Stars come in a 650cc model, and Suzuki makes both a 500cc and 750cc bike that serve as wonderful starters. All three Companies make a 250cc starter bike, but if you plan on taking a penger anywhere or doing a lot of freeway riding, go with at least a 650cc bike. Also, try going to a dealership and sitting on a few bikes to see which one fits you the best. Be safe and enjoy!