So airsoft as a whole can be very expensive or just slightly expensive;) Purely depends on two factors in my mind, the type of game your playing, and your personality.
On the type of game, typically a milsim style game is going to require more gear, and guns than REC style games. You also may need multiple camo patterns to be able to play on a particular team etc. And in that case you may also invest in multiple gun platforms for various teams if you want to take it that far. And yes you can do milsim cheaper than that, and some guys do but most of the guys I see who take milsim pretty seriously spend a fair bit of coin on guns/gear.
Your personality if you like to collect guns, and enjoy the new best thing. Resale value on airsoft guns in general is pretty poor, and it's related to reliability which is also rather poor. So if you're going to sell your existing gun and buy a new gun every few months you're going to loose allot of money doing it that way. If you keep things, can work on them and buy smartly with used guns it can be cheaper to feed the addiction;) Also if you track towards say sniping, then it can be pricey not only in the gun but also the ammo. If you stay more near the normal guns/ammo things are cheaper there. If you go say support gun again ammo costs are going to go up as well.
So it depends I'm somewhere in the middle, I don't have allot of gear but a fair amount of camo. I use tan gear, it mostly matches most camo well enough that I don't need duplicates there for most team setups. I run typically AR platforms now, all different sizes and setups but they all share magazines. Also they all use the same mag pouches, so I can setup for a short AR, mid range, or even my M16A2 which is a bit of a sniper rifle in it's current config. Gun wise I've sold allot of my more oddball stuff and replaced it with AR platforms because of mags and pouches. I dig odd guns but I don't need to collect even more gear than I have now. And I try to limit buying the new cool thing if possible, and rather buy the new cool thing once guys get tired of it and move on to something else;)
Another important bit in my mind, if you're mechanically inclined it's much easier to do your own work on guns. Then you can save some money(not time at all), and get inexpensive guns and tune and work on them to get good results. Especially used possibly broken guns, depending on what is wrong with them and the price. But it's a two way street seldom will you get a gun with only the problems disclosed being the problems. Often I find other stuff wrong I didn't know about until breaking it down, etc.
But it can be cheap or expensive depending on how you do it. I'd say run whatever works for you, if you're not being seriously outgunned, I'd hold and decide which direction to take it.
Luke