Well cheap to most of us. You can spend a lot if you want to, but you don't need to. But finding, and importantly organizing, makes for many restful hours.
My father was an avid collector and spent many hours cataloging his collection.
I will say though that as a whole, a collection (and indeed any collection, not just stamps) has almost zero net value. The cost of selling the collection dwarfs the collection value.
My advice to collectors is to have as much fun -selling- the bits in the collection (-especially- the valuable bits) before you pass. Do Not expect your heirs to sell it; they'll basically take pennies for it just to make it go away.
My father sold (or separated out) everything of value so we could dispose of the rest (basically donated to a dealer) with a clear conscience.
So I encourage collectors to take this advice! Set aside anything you'd want your family to try to get value for, separate from what you're okay with them letting go.
(Possibly as a consequence of this, my collecting tendencies tend towards things with intrinsic value such as tools -- I tell myself that at least selling e.g. a hammer at a yard sale should be easier if you don't need to find someone looking for a one-of-a-kind mis-forged XYZ brand from October 1965... Definitely not expecting anything to be a store of actual value, though, and I'm sure my heirs will feel burdened no matter what they end up having to deal with in my estate)
Of course that's great for everyone who collects them without expectation of profit.