It is my firm conviction that it is possible to decorate with style without breaking the bank. You shouldn't have to fork out thousands—or hours upon hours of your time, either—just to get some nice decor on your walls.
Make a List
Are you on a budget? Or maybe you aren't, but should be? We've all been there. Figure out exactly what you want, make a list, and stick to it—this will keep you from being swayed by the beautiful displays at your favorite stores that you can't afford and that wouldn't work for your home anyway. Do your research beforehand and create Pinterest boards. Oftentimes, it takes months to accumulate the decor you want when you're doing it on a budget—whether that's because of monetary constraints or because you don't have time to bargain hunt multiple times per week to find exactly what you want. So, prioritize what you need to get first, and be willing to play the long game for the rest of the items. Sometimes, if you wait, you'll end up getting exactly what you want for sale, anyway.
When you buy digital art, you're eliminating shipping costs. If you don't mind printing it yourself or having it printed by a local service, printables can be a great way to go. You can always buy a black and white printable, print it at home, and mat it with some patterned or colored cardstock. Printables also allow you to get your piece printed in unique ways, like Fracture, which prints your piece on glass.
Look for Free Art
If you're willing to get on an artist's email list, you can often find free printables on Pinterest. Respect small businesses, though, and don't "dine and ditch"—i.e., don't unsubscribe as soon as you get your freebie, that's just dishonest. Find an artist that you genuinely would enjoy following, and enjoy your freebie and subsequent emails.
If you have a few spare minutes to go on the hunt, my favorite is old public domain textbooks that have been digitized. The biggest resource for this is the New York Library Digital Collections, but you'll have to flip through pages manually to find what you want. I've had prints from this site on my walls for years! Old Book Illustrations is another great resource, and it is more searchable. There are a lot of great results under "botanical."
Buy Frames in Bulk
Framing is often the most expensive part of wall decor. Buying online allows you to price check, but especially for larger frames, you'll incur added shipping charges. You can buy an entire gallery wall's worth of frames all at once, like these ones, and use them in different parts of the house—you don't have to use them as a gallery wall. Or you can buy a bunch of the same sized frames, and save some for great backup gifts later on.
Add Some DIY Elbow Grease
IKEA's frames are some of the cheapest around—I always stock up when we go, since we don't have a local warehouse. Unless you're shooting for a minimalist appeal, they can be a bit plain—so dress them up! I've done this with frames from the Dollar Store, too.
Or, don't buy frames at all! Use Washi tape in place of frames, or mount some nifty binder clips to your wall with sticky tack, and clip different pieces of art up as inspiration strikes.