With the exception of a very very few people that go and win every 40k tournament to build their army ( I don't know anyone who does, but I'm sure someone one has or is doing such a thing ) with prize support, most of us have to "invest" in models to get our 40k fix.   So the 3 most popular takes on this are the following:

1.  Buy brand new ( retail price or standard 20% discount )
2.  Buy 2nd hand ( ebay, bits traders etc )
3.  Buy " counts as" and raw materials to make your own

I personally use all 3 strategies to build a army as it prevents total wallet drain and enables some personal flavor to be added to the army. 

Now this cost is not including paint, any custom bases or flock, tools ( brushes, air brush etc ), and most importantly time.  The Ebay route can help as most complete armies are painted and based , but as an average your looking at $1k and up for a decent 1500 point army .  Raw material route is cheapest, but usually involves the most time as you now have to make the part and than do everything else you would of had to with a new model .  This gets further OMG by the meta being infantry vs large vehicles or models. So now its 150 guardsmen to build and paint, not 4 tanks.  That's a lot of time ! and time = money!

So If most don't know I have many vices and 40k has been a great one as it WAS not the most expensive. ( Cars and racing will put any 40k budget to shame ).   GW will be increasing prices again like they have every year. $90 for a storm raven,  $60 for a 5 man terminator squad, $65 for a Maulerfiend.  These will go up slightly and if not something else will. Meanwhile our taxes rise and we have less disposable income for hobbies ( that is if you are lucky to have a job ).  So lets price out a new army list that was posted recently on Whiskey and 40k ( Mike Brandt's blog ) as you can be sure it will be competitive, fun, and Mike is a master list builder.

 Sammael on Corvex - 200 ($40)
Librarian w/ Bike, Auspex - 90 (Warlord, more often than not, b/c I'd rather a shot at the other traits than what Sammy has)  ( $10 bits converted bike )
Primaris Psyker - 70 ($14)

Ravenwing Command Squad w/ Bolterbanner - 185 ($40)
Ravenwing Command Squad - 120 ($40)

10 x Tactical Marines w/ Heavy Bolter - 150 ($30)
6 x Ravenwing Bikers w/ 2 Meltaguns - 181 ($70)
6 x Ravenwing Bikers w/ 2 Meltaguns - 181 ($70)
6 x Ravenwing Bikers w/ 2 Meltaguns - 181 ($70)
6 x Ravenwing Bikers w/ 2 Meltaguns - 181 ($70)
6 x Ravenwing Bikers w/ 2 Meltaguns - 181 ($70)

Platoon Command Squad - 30 ($38)
Infantry Squad - 50 ($23)
Infantry Squad - 50 ($23)


So total without paint or anything else that you may need is roughly $608 discounted and not GW pricing. 
Not bad, but add 2-3% and you're at $626 for the next GW increase average.  This would be ~$750 from a GW store if not more. Still not too bad for what it could do, but your almost talking $1k!!!!Add in some Terminators or maybe a heavy support choice to buff the list and there you go.  So now you have a snazzy new DA army for $650 lets say and another FAQ and codex comes out and makes an ally or another unit in the dex too much to resist.  So let add in another $70. Now you find that GW has nerfed a unit in your dex and made it almost unplayable (This has happened more than once ). So you can salvage what you have, but add in $300 to be top tier playable.  So this maybe the course of 6months for a gamer.  This again doesn't add in costs for RTT and GT entry fees which can go about $100 without room and board.  Travel is another thing to look at even if your not flying.   Oh and don't forget a case and new foam. WOW!  that is a decent investment.  Now if your like me and have a few armies times that by 2, 3, 4, 5 ......

So why talk about this?  Well cost will influence the game as not everyone will have enough to go and buy the latest greatest toy.  The Meta will be what people are playing.  Some people play the same army and have been for years.  Well congrats!  I never could eat the same thing every day so why do the same in gaming if I have a choice.  The cost will cause people to stop playing as food and a home are more important. The less people that play the game the closer the game is to dying exponentially. Things aren't getting cheaper and I have been blessed with the ability to make enough for silly things like 40k to be in my life so far. Some people do not and will not invest in this game if it keeps on the current trend and just that the fact I'm thinking about it makes me wonder if I should get in the latter category.  Guess I'm trying ask what is the breaking point for the 40k player?   and are we there yet?  Is $1000 acceptable for a 2k army? Do we get $1000 of fun from this?