While I think prices are crazy (like painted helmets, most of which are probably fake), I would like to make the point that it's only collecting SPECIFIC THINGS that is a rich man's game. Sure, you want uber special-combat-commando-death from above-named and used in combat stuff? It's going to cost you- due to supply and demand as the demand is ultra high.
But if you collect something that is not at the top of the pile there's lots of stuff that can still be collected for cheap. You can walk into a show and for little money buy some nice things if they are not something everyone else is buying. And in that knowledge is power. If you know what you are doing there are always undervalued things on dealer's tables that they don't realize the value of it.
Part of this is the old collectable rule of 'collect something no one else does, amass it, write a book, then sell off you collection.' Case in point: old metal lunch boxes. Once the book has been written interest goes up and prices spike.
Yes, you should collect what you are interested in, but collectors, especially young ones, should at least consider not following the crowd. If they look around (and read books on military subjects that are not just collector's books) they may very well find something that is interesting, and for the cost of a "pistol belt used by a paratrooper" can acquire a very nice collection of items that may just be sitting in people's junk boxes.
Maybe that means from a time period folks aren’t interested I much. I see some really great cold war material for cheap. Navy items are still pretty inexpensive. There's a lot of small home front dohickies that are passed by as 'not being a combat item.' I am astounded at the low cost of some of the post 2000 military items on the market. Most of these guys are still around and could probably tell some great stories- a gold mine for a young collector. It could be another country's items; how many people collect Canadian items used in peacekeeping missions? You could collect variations on WW2 canteens and end up with a great collection of different makers for the cost of one "combat used" helmet.
I am reminded of a fellow I took to his first show who wanted to collect German stuff. After looking at the prices, and realizing the minefield of fakes, he started collecting German railway insignia. He picked up items that no one was reproducing, for a very low price when everyone else was looking at the iron cross 1st class and trying to decide if it was real.
I guess what I am saying is keep your mind open and don’t feel you have to follow the crowd. Strike out on your own. Find an area no one knows much about and do the research to make it your own area of expertise. If you have to collect WW2 combat infantry consider specializing on one division or landing in the Pacific. Or what about the coast artillery, or AAA units, or … the list is almost endless.