I've heard a lot of good things about the H&R Pardner shotguns. I personally don't have one, but I'm picking up a Rossi youth single shot .22 /.410 in a couple weeks for my step son. Having handled both a new and a used of that model, I have to say I like the Rossi also.
I'm sure you'll get asked questions by others, so I might as well ask them myself.
What are your plans for this gun?
Why the 12 gauge and not another?
I have a single shot 20 gauge that is probably older than I am. It's accurate (proven yesterday evening against the darn ground hogs tearing up my yard), relaible, easy to break down, etc. Lots of good can be said for the old single shots. Spent $79.95 for mine.
My LGS has a lot of single shot shotguns on the used rack. Most of which are in the Sub $150 range.
As far as anything blowing up in your face, the odds are astronomically low that any gun will do that.
Also, considering your price range, I'm sure you could pick up a used pump. Something like a Mossberg Maverick 88, or a Remington 870 Express, or even the H&R Pardner pump.