Headphones for isolation

The 202 isolates surprisingly well for a supraaural... if you can get the fit right. But the sound is so-so (bloated bass) and I found it downright uncomfortable. These are phones I like to loan away. :-)

For home use, full sized cans generally are much better than earbuds.

KSC-75 will have little if any isolation - it's an open headphone design. (Hold a playing card over your ear; it'll be about like that.)

If you need maximum isolation, in-ear monitors generally beat full-sized headphones. (There are exceptions: the most isolating headphones (Senn HD280, say) isolate more than the very least isolating IEMs (Sony EX71 or Panasonic RP(whatever).)

There are a very limited number of choices under $50. In headphones, I'm not familiar with the HD202 but I'm a fan of the HD201. Good sound, but not a lot of isolation. In IEMs, under $50 you're probably stuck with the Sony EX71 or EX81 or the Pana RPwhatever. None of them are terrific, but IMO the Sonys are tolerable-to-good at the price (others disagree; the EX71 was a favorite whipping-boy around her for a while).

Stretching your budget to $70 or so will get you the Shure E2C IEM, which is a big step up in isolation and, depending on your taste, a step up in audio quality as well (though its highs are pretty rolled off).

To get serious isolation in a full-sized headphone you're looking at $90-$100 for Sennheiser HD280 or HD25-SP. (I like the HD25-SP more than the HD280, but I'm in the minority.) For that much money you could get also get fancier IEMs than the E2C, such as the Etymotic ER-6 or ER-6i, the Altec Lansing im616 (has Etymotic guts), or Ultimate Ears Super.fi 3. I'm not familiar with the UE, but the Ety-based products are quite respectable sonically, as well as providing very high isolation.