After reading through most of this thread I decided to contribute my 2 cents.
Based on the OP's budget and experience, I would give another thumbs up to the Kel Tec Sub 2000.Before moving back to Mass I owned 2 different configurations (Glock 19 & Beretta 92) and loved them both. Put over 2000 rounds through each of them and only had a couple of hiccups with one of them early on while "breaking it in". Other than that, they were perfect. Although not "tack drivers" I could hit a tuna can lid (tacked to a stump) 4 out of 5 times (if it didn't fall off the stump) at 100 yards with the open sights they came with. I know some on this forum don't care for their sights but, aside from them being plastic, I found them to be more than passable.
Even this carbine though, might be a little over powered for home defense if the bedrooms in your house are in the line of fire or your neighbors are too close. The 9mm versions (recommended) hit like a point blank .357 mag at 50 yards.
Accurate, reliable, folds in half for storage/transport...priceless.
They can be hard to find if Kel Tec's annual production run ended more than a couple of months prior to your search. The GB posting that was offered up earlier in this thread ended without a bid and it had a $399 starting price. So I would guess they are available now.
They can be had in models that accept mags from Glock 17 & 19, S&W (can't remember which) and Beretta 92 (and 9000 I think). So if you think you might add a handgun to you collection, pick the right model and you'll be able to interchange mags between them.
Some find their ergonomics wanting. Short pull, cold metal stock, charging handle tough on the fingers...but there are cheap, effective accessories that take care of those issues. Some from KT, some after market.
Good Luck.
P.S.
KT warns against pulling the trigger while the carbine is disassembled. They say that if you do you'll need to send I back for repair...NOT TRUE! You can easily reset the trigger with a dowel with the gun in its" folded" state.