RE: Installing open sights
$600 is too high for a rainy day rifle. I hear you, though, on the subject of the Mossberg ATR. I guess I'll continue to keep my eyes peeled for a cheap pawn shop rifle or rifle range rifle -- a British .303, a surplus mauser, or better some .30-06 surplus.
In three years of deer season I have been rained out 1.5 days. Not a big issue, so I don't want to invest much in this rifle.