Good and Cheap PCP

CZ200 S. Great rifles and super accurate. It's does many things well. It is lightweight and not a burden to carry hunting. At the same time the stock is target oriented. The accuracy is outstanding and can do well in the shooting sports like field target or down tuned for 10M. They are very effeciant with air consumption. I have 3 of them and all get 58 accurate shots in a 25 fpe spread. They are a gun of choice for kids as they are so easy to shoot. I do like Marauders and have shot and worked on them quite a bit. I just find the CZ200S (AA200S) to be the better shooting rifle. You don't need to work on them or buy after market stuff to get them to shoot great. Just buy and shoot.
 
Unless your 13 year old is a Neanderthal, the Marauder is going to be heavy. Ok for bench shooting but offhand will be about impossible. The discovery or Maximus are good long rifle options but I still think the P-rod with carbine stock would be best. The stock that comes with it would be fine after some modifications. Some pipe insulation makes a good cheek weld, some hooks bolted on provide a place for a sling to attach. 
 
The Hatsan ATP2 QE is a great starter gun. It's light, cheap for a PCP repeater, can be used as a pistol or rifle and has removable cylinders so a spare can be carried. 

The Sumatra carbine is worth a look if noise isn't an issue. They are light, powerful, accurate, adjustable power wheel and make you feel like a cowboy. Loud enough to wake the dead though. 

The Marauder pistol is a great option as other have said. 

I have all of these three and I am sure any of them would meet your sons needs. Walmart sells the Marauder pistol for just $350 so it's practically free :)
 
Good and cheap don't often go hand in hand, but I think the benjamin discovery others have recommended is a great choice. Most air rifles and PCP's especially are heavy beasts. The disco is light and compact. Comparative to something like a Ruger 10/22 if you're familiar with that. Good for youth but still very fun for adults. I still have fun with mine even though I have some high dollar rifles.