Cheapest 6.5x55...
Silver Bullet 12--The least expensive entry to the world of the 6.5x55 would be to find a Bubba-ized Swedish Mauser at a gun show. The Swedish Mauser has the nicest workmanship of any of the "common" military Mausers--and very nice accuracy to boot. Doesn't matter where or when it was made, either--They were all well made, out of xlnt Swedish steel.
Now, if you can find one that Bubba cut down the stock of--crudely, you hope (ugly is cheaper)--without messing with the internals, it won't cost an arm and a leg, but it'll work just fine. If Bubba also did a decent job of mounting a 'scope mount, bending the bolt, and modifying the safety, so much the better.
I lucked in to one just as described, bought it, sighted it in during the week, and took it out the following weekend and killed the largest doe I've ever seen. (No, this wasn't an edition of "The Last-Minute Deer Hunter"--I DID have 2 rifles all sighted in and handloaded for, to go deer hunting at the time!)
Last fall I lucked in to another, at a pawn shop; offered less than they were asking, and they took me up on it. To a collector, it'd be a horror show. Its stock was "cut down" (ugh!) and a Pickatinny rail had been installed over the receiver. All the blueing had been sanded off, and the rifle coated with some kind of clear preservative. Bolt was bent, but the safety still unmodified. It looks funny, but if it'll shoot decently, who cares. I stuck a red-dot sight on it, that avoids the area of the safety. That one I haven't had out shooting yet.
My point is, that Bubba'd Swedes are to be had, they are cheap, and still fundamentally dependable.
Handloading works fine with the cartridge. With my deer-hunting Swede, I didn't have time to do so, therefore used ordinary Federal blue-box ammo, the cheap stuff. Worked slick.
The 6.5x55 is a GREAT deer round; nice accuracy, good penetration, low recoil. I started my own son on a .243 Win, but he was slender and small. If your boy is an "average" 13-yr-old, the 6.5x55 oughta work very nicely for him. You, too, will appreciate the low recoil.
Anyhow, enjoy the hunting with your son--first of all for a Swede, then for a deer!