I think that sometimes the price can be high for different reasons.
For example, you can get guns that are good for long range, short range, mid range, having a high fire rate, some guns might be really rare, or super common, have a lot of spare parts, or hardly any etc etc. The best guns in these classes are going to be highly expensive and if you're not wanting to buy it for the reason it is priced so highly, it's going to seem really unduly expensive.
Say, if you just want a general purpose AEG, that's good for everything and you start looking at something built for sniper range and accuracy built into a carbine sized package, then you're going to find that the gun seems stupidly expensive. That is the general difference between say, a CYMA and a Systema.
I think that with some guns though, they sort of get this reputation for being really good at something from a few people and it just sort of spreads around and people get brainwashed by it. I call it 'Tokyo Marui Syndrome', due to how everyone I talk to says Marui's have immense range and are the best guns out there, but to me they're just crap. They're plastic, which I hate (when anything else is plastic, it's cheaper because plastics are cheaper than metals, so why does Marui get away with being MORE than most metal guns?), they're sub 300fps which I hate and the range on them is appauling, I don't care what anyone says.
People are brainwashed by expectation. Also, higher fps does give more range, it's a simple physical principle. The more force there is behind something, the further it will go. Sure a good hop unit helps, but a Marui hop unit at 300 fps is not going to match an equivalent hop unit at 350fps, or even 301fps because the extra force does stand for something.
ANYWAY, I generally agree that you get to a point where the guns are stupidly priced. I would never pay £1500 for a Systema when it's possible to upgrade a £150 AK (or anything else for that matter) to have the same performance for a fraction of the price if you know what you're doing.
Once you get past the £600 mark you're just paying silly money. But up to £600 I think you are paying for quality products, good parts, nice materials, well finished, functional etc. Once you go past £600 you're just getting the same thing, but for more than £600.
I think Systemas are 'sort of' an exception because they're built for the purpose of military training from the ground up and since they're being marketed to a governmental institution with a seemingly unlimited budget, they might as well milk it for all its worth. I know I would if I were producing Systemas.