Warhammer doesn't need to be an expensive hobby: Poorhammer is here to save your wallet
Go by official prices and you'll get the wrong idea about how expensive it is to get into Warhammer. None of the armies being brought out weekly at my local wargame club cost full price. Between third-party retailers, mail-order discounters, Facebook marketplace, secondhand stores, bootleg Chinese recasts, 3d-printing, and going halfsies on a boxed set with your mate who wants the space marines when you just want the tyranids, it costs less than you think to put together an army of little guys. You can even make them yourself.
This is what the Poorhammer community is dedicated to, and it's an inspiring example of DIY ingenuity. One of my favorite examples is an ork submarine made out of cardboard and rubbish, with a Pringles can as a significant part of its structure. Orks are a gift to the Poorhammer player, with their junkyard aesthetic perfectly suited to modeling things out of leftovers, as is the melty and mutated vibe of a Chaos army.
Terrain is the other thing you can easily make on the cheap by recycling rubbish. The traditional Warhammer hill is two or three layers of packing styrofoam glued together and painted green, but I've also seen a lot of ingenious things converted from spare sprues after miniatures have been removed from them. Cut those up and glue them back together and you can make excellent brick and plank walls, as well as the ruins and rubble delightfully nicknamed spruins.
Old heads will remember when Games Workshop's White Dwarf magazine encouraged using stacks of books to make hills and contained a template for making a cardboard Baneblade tank, as well as showing off a grav tank made from an old deodorant stick. To be fair, they're still on board with this kind of thing, even posting on the Warhammer Community website about how to make your own unit fillers.
(Tournament players may get their knickers in a twist about unofficial models, but the competitive scene is its own weird niche and it's best to pretend they don't exist. Nobody at a casual gaming club is going to complain about your proxies and "counts as" substitutions.)
Though the prices are way out of date and the whole thing's been consigned to the Internet Archive, the Hipsterhammer blog used to be another great source for ideas about building a Warhammer army on a budget, with suggestions on cheaper minis you could substitute from other manufacturers. Glue some spikes on Vikings from a historical wargame and put them in your Chaos army, why not? It was also an excellent source of inspirational mood boards and maybe the most insightful thing ever written on Slaanesh.
Games Workshop is adamant that Warhammer is more than just a game—it's a hobby. Assembling and painting and kit-bashing an army of little guys, they say, is as important as putting them on a table and rolling a million dice to figure out how many of them die. Inevitably that leads to players thinking about all the ways we could save a few bucks by doing it ourselves. Poorhammer DIY projects are just another part of that hobbyist spirit.
You know, I've got an old deodorant stick and some spare bits of an old model ship lying around. I really should make a grav tank out of them.