The days of the low- to medium-budget film seem to be over, at least in moviehouses.
Exploitation movies began in order to "exploit" topics that mainstream Hollywood couldn't or wouldn't touch. Opening weekends were largely beside the point when you had a movie that could be played and replayed for years at grindhouses or drive-ins.
The exception was art houses, the owners of which bit their nails every time they took a chance on an untested title, but there aren't many art houses left any more. (And it's why a lot of art houses kept rebooking the same tried and true movies once a year or so; they knew people would come back to see them, especially since most of them weren't available on home video yet.)
Cable, PPV, streaming, DVD -- those are about the only places to see what you're talking about, OP. That's a shame in some ways, but it's also a benefit in others, especially if you live in a small town where those movies would never play in a conventional theater.