Re: good(cheap) bike to start with? wally-world?..
The suggestions for a used bike are sound but keep in mind that you'll need to go through it and make sure parts like bearings and brakes are up to the task of a motor. A popular bike that you'll see often here is the Schwinn Jaguar. Regular price at Target is $149. but often on sale for $124. There has been some talk about the Jag being discontinued but I also understand that the South Port is replacing it. Same bike, different color scheme. However like was stated above the cruiser style frames are a little harder to mount an engine to and the older 'V' frame road bikes lend themselves to motorizing quite well especially for the newbie . Good luck and let us know which bike you decide on....and send pictures.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"