Is this gun going to be used for home protection only (not concealed carry)? If so, then I'd recommend a used pump shotgun over a handgun. You still have to aim a shotgun, but it is much easier to hit a BG with a long gun than a handgun. Used Remington 870s can be found for under $225, and used Mossberg 500s or Maverick 88s can be had for as little as $150. Very inexpensive, very reliable and a heck of a lot better at stopping an intruder than a puny handgun.
Yes, I like my S&W 686 loaded with 38+P at my bedside for quick access (I keep it in a GunVault - I've got a 2 yr old). But if I'm able, I'll be making my way to my closet to grab my 12 gauge. I feel much more confident in its ability to stop an attacker than my S&W, even if it were loaded with 357s. Nothing quite like hurtling nine 33 caliber lead balls at a BG with a single trigger pull.
That said, I agree with others who suggested a used S&W 9mm auto. Doesn't even have to be a Sigma, I've saw a ?5906? in ?9mm? recently for $199, though most I've seen are in the $250 range. I saw a used Glock 17 a few months back for $375, and a Ruger P95 for $350.
A semi auto will work for a beginner, but keep in mind that many a gun noob (and even some more experienced) have unloaded a semi auto "backwards" ... racking the slide then dropping the mag. Just be sure he knows in his sleep to do it the other way around!
In the end though, the 22 would be a very good place to start. My sister recently acquired a Ruger Mk II for $199. This way he can build solid shooting techniques without concern for recoil. On the other hand, for home protection my sister got a VERY sweet 4" S&W 681-3 in .357 Mag last year for only $350 ... and proceeded to shoot 2" groups at 7 yds in double action all day long with it!