I think I would be classed as a bottom feeder in the air gun world. I do have a few "nice" rifles however. I think the biggest difference you will see is in the triggers, that is the most easy to see.
IMHO .5 at 50yards is very doable with an "entry level" PCP. Moving out to 100 yards (again IMHO) there are several things that come into play. First off is just what happens to pellets when they move past the speed of sound, and then cross back over again. From what I understand it does the same thing to bullets, but cranked up to 11. The shuttlecock profile of pellets just does not like going that fast and then slowing down again. So you are going to be generally speaking in the 900's FPS as far as speed goes, so you are going to be dealing with a bit of drop. Personally I have seen pellets shoot fantastic at 50, but like hell at 100, or even 75. This is why many airguns that go that far out are shooting "slugs"....or really bullets, and you do need a barrel that is specifically for slugs. I have never seen a barrel do real well that shoots both.
Again generally speaking you are going to want something with a regulator on it, this will give you best ES....usually.
There was an entry level european version of an airgun (under 12FPE) that shot just fantastic. I bought one and it does work out to 50 yards just fine, but farther then that it is just too slow and too much acting on the pellet.
Bottom line is you don't have to spend a ton of money to get something accurate at 50. Personally with the (at least) dozen air rifles I have you will not be happy at 100 unless you move to something that will shoot slugs. And that moves into a very different area. Ammo selection is everything.
Here are a few pics of ammo testing indoors, so no wind. The gun was on the bottle, so no real loss of pressure. The differences in the different pellets is staggering. The first two is the difference between 4.51 and 4.52 pellets, one would corkscrew like a mad man. I would have never thought that .0x would make that kind of difference. Each group it 5 rounds, yea not enough to really tell what is good, but enough to tell you what is not good, so you don't waste your time on it.
Years ago there was a web site, I want to say shooters world, but could be wrong. That would do a pellet sample box. They would sell you basically a tray for fishing, and each compartment was about 25 rounds of all kinds of different pellets from all kinds of different brands. H&N, JSB, you name it, that pack had it in there. It was a great way to find out what your gun likes if you don't have a large sample of pellets.