A good cheap engine for a noob would be any O.S engine, or Dynamite 12spd is another good one.(The Dynamite is all I run, but I mod them first)
O.S. has the reputation for being solid, consistent, and reliable for a fair price.

The Dynamite doesn't have an over-abundance of power in stock form, and is a nice, reliable, easy to tune mill. Bonus on the Dynamite is the con-rod is knife-edged, and the ports on the sleeve are just begging to be modded. When done right, it gives it more punch in the mids, and plenty more revs.(when done wrong, it only costs about $40 to try again)