Wait, is affordable cosplay a thing? Thankfully, for the sake of your wallet, it is! Some of these won't be applicable to everyone, but many of them are.
Buy second-hand
There are two Facebook groups that are great for buying a cosplay second hand. It can be a bit confusing since both of them are literally named "Cosplay for Sale!" They're both a solid resource for cheap cosplays. They won't have some cosplays you're looking for, and sometimes the buying process can be a bit quick, but you can find some great deals as long as you keep an eye out.
My entire Runa cosplay (except the shoes) came from one buy in one of these groups. I'm not really happy with the wig, and I do plan to get a new one some day if I decide to keep cosplaying her, but I wore her to two cons and had a blast. Whenever I get to host my Kakeguri panel I make sure to bring her out to interact with some folks and she's always a hit. Plus her coat is super cozy and well worth the cost of the entire cosplay. I do want to modify it a bit but it's super warm and comfortable.
If you're looking for more common pieces to put the cosplay together you can go to Goodwill or an online thrift store. The pants for Kim Possible and Jack Frost are from Goodwill, the Jack Frost shirt is from an online thrift store, and the Chloe Bourgeois shirt and sweater are from the online thrift store too. The downside with buying second hand online is that you can buy something not quite right. Say it's too thin or it is smaller than you expected. You'll need to return it or replace it.
Modify a piece instead of buying it from an expensive retailer
A lot of basic pieces can be modified. My black dress that I wear for Mavis was originally a large t-shirt dress that a friend helped me to alter. I did need help for this one because it was being taken in on the sides and in the back and I don't own a dress form, but it ended up costing me about $15 and spending time with a friend. For my Mavis shoes I dyed some white PF Flyers that my high school boyfriend had given me back when we were dating red. They came out more pink, but hey I only spent about $5 on those. I had the shoes already and honestly wore them maybe once per year. Maybe. For the arm sleeves I literally took a $2 pair of tights from Walmart and just cut holes for my hands and head.
Share cosplays with a friend
I'm aware that not every friend group can do this, but at the very least you can buy uniforms that two characters wear and just swap wigs and accessories. It's an easy way to have more fun as more characters. It doesn't have to go both ways, so you could just borrow a cosplay. But if you borrow one then you need to be open to be open to them borrowing one from you or wanting to swap one for a con.
Do be aware that you'll need to be similar sizes to borrow a full cosplay and that you'll need to be careful to not damage their cosplay. If you do damage it, it's best to offer to replace it or pay for the damage. Kinda the "you break it you buy it" mentality.
Do multiple outfits for the same character
For Ochaco I have done her sports uniform, a bikini look, a Christmas look, a few casual looks with things I already owned, and a kimono look. This allowed me to save money on wigs, and for the Christmas look I can wear it for any Character that I already have.
Do casual cosplays
Never under estimate the power of the right wig and makeup. I've seen a ton of Katsuki Bakugo cosplayers get away with wearing the wig and then just some gym shorts and a white tank top with chunky sneakers. All they have to do to complete the look is sneer at a Deku and stomp.
I've done casual looks of most cosplays as well, for that I'll just pull pieces from my closet that I already own and then slap on a wig and the right makeup. Easy!
Use pieces you already have in your closet
My casual Ochaco was just the cost of the wig and a stronger blush. I already had everything else in my closet. For Kim Possible I already owned my boots. For Mavis I already owned the shoes, I just dyed them. And no one would know except I just told you that now.
When I did my first look/casual yet sexy Soi Fon I used a onesie top that I already owned. I also already owned the socks that I wore. If I ever do a formal Soi Fon I'll wear a beautiful black dress that I already own. I actually have a number of black dresses or jumpers that would work well depending on the vibe I want to go for. A clubbing look, a modern-50's-flirty look, and the formal dress. And black clothes aren't hard to find so I can easily do casual looks.
Become a horder
I have never gotten rid of a cosplay. Now granted I've only been cosplaying since May of 2017, but none the less I've never gotten rid of a cosplay. I don't wear some anymore since I put them on hiatus, but I still have them. This means that if I ever want to bring it back then it's ready to go. This also means that if someone wants to borrow a cosplay I have then it's also good to go and ready to be brought back out.