Cheapest way while having some reliability?
This BGF kit: http://www.ebay.com/itm/80cc-Bicycle...item257d1f5f10
With this Huffy Cranbrook: http://www.walmart.com/ip/26-Huffy-C...-Gold/23267977
Definately get this or something like it for the front wheel: http://www.amazon.com/Pyramid-Mx1000...bicycle+brakes
Also get a chain breaker so you don't need to use the tensioner, and later on down the road switch to a sprocket adapter like this: http://www.piratecycles1.com/picycbspad.html
On any bike I get, especially wally world bikes, I take the entire thing apart and re-pack every bearing with some top quality grease. This can save you A LOT of trouble and pain down the road.