I've seen a lot of focus on this since I've been paying attention to Facebook more. Feel free to swing by my Facebook page by the way, I'm working on building it up. Anyway, I've seen this focus on "witchcraft on a budget". Unfortunately, I mostly see the same things. Lets dive a bit deeper, and see if we can't get you all saving a bit more money.
The easy stuff
This is all the stuff I usually see. I could just as well share any number of things other folks have written, but this way you don't have to dig for it. Dollar stores are a theme.
Nothing wrong with herbs and such from the spice racks. Heck, most of mine are from the grocery. Dollar stores even have the basics. I do suggest that your stuff is more effective if you're not using herbs that are super stale though. Herbs have a shelf life of about 3 years, or at least that's what McCormick says. Don't go out of your way for fancy ingredients. You could practice magic effectively the rest of your life with nothing but the dollar store stuff.
Birthday candles are fine for basic spellwork. They don't carve on well, as there's just not enough space, but other than that, they're cheap, and come in many colors. I even reuse the candles that were on my birthday cake for spells related to my birthday wish.
Dollar stores have glass enclosed candles that last several days for like $1.50. Catholics and Ex-Catholics are probably quite familiar with this style of candle. These are a slightly different way of working than the chime candles many of us came up in our practice with, but they're probably my preferred type of candle now. I'll put together a whole article about them at some point.
Wildcrafting - So I'm a big fan of wildcrafting, or getting things for free from nature. The only thing I'll say here is you want to make absolutely sure that you know what you're getting. You also should learn to dry herbs and plants properly. Wildcrafting is a skill that can be very useful, but it's a skill for sure.
What I rarely see
There's a handful of tips that I never really see talked about. Some of this requires a bigger investment once, but will have long term benefits.
Buy in bulk where you can. Things are cheaper in bulk. Herbs and such, oils, anything reusable is cheaper in bulk. If it doesn't go bad, then there's no reason not to buy in bulk. If it does go bad, you can split bigger packages with one or 2 other folks if you know people.
Find the multipurpose things. Make good friends with herbs like cinnamon, rosemary, and the like, that have wide ranging applications. Means you need to keep less variety around to feel properly "equipped"
Focus on reusable symbols. I collect keys and a couple other magical symbols that are quite reusable. Not only can these be cleansed and reused in most cases, but in most cases this symbol will become more powerful.
Buy a printer! Getting into seals and sigils and things like that are a simple way to do magic on the cheap. A printer extends the options and also can pave the way to the next step here. This one is kind of expensive to start with, but pays off pretty big.
Learn to craft your own things. This can get expensive if you try to do it all at once. One thing at a time though, this isn't so bad. I've written on making your own oils, and black mirrors, but this is one I'm actually a big fan of, and I'm sure I'll walk ya all through more as time goes on.
Other things to think about
So there's 2 streams that go into most modern magical practice. Remember that the idea of the middle class is pretty new. Back in the day, folks mostly either had money enough to not worry about it, or had like nothing. There's almost 2 currents to magic here. The first HAD to use what we had, and the second had enough money to make finding a special ingredient it's own layer to the Work. Understanding the 2 currents here, and how we as modern folks that are mostly in between those integrate them is pretty important. The way I see it is this. Sometimes our "stuff" is important. But it's not about what we spend on it, it's how we treat what we're getting. Dollar store herbs work as well as fancy stuff from the metaphysical store, but neither will work unless you've prayed over them, charged them, and made them symbolically important in your work. That last part is the point here. Did you phone in the gathering of your materials, or are they symbolically important? THAT makes the difference here, not money. Look around your world, and decide what you already have that IS important to your magic. The best magic is created not by what you spend, but by what it means.