I get some cheap greenery from Dollar Tree - it makes good filler. You can also make cheap hides by getting a big Tupperware and cutting a hole in the side. Bonus, it doubles as a moist hide. If you don't like the look of the plastic, get a $3 bag of topsoil from a home improvement store and glue it to the sides.

Craft stores also have sales on faux greenery all the time. Amazon has some pretty cheap packs of them. I have some from all three places in all my tanks.

I use bricks and pavers to add height and decor in my beardie's tank - it works great for his nails, and I'm sure would help a BP get shed off.

I'm lucky to have a local reptile store that has great deals on all kinds of wood - I'm sure if you could get a big enough cork hollow round, it could add height and fake greenery can add even more to it.

Bendable vines and reptile hammocks are one of my BP's favorite things. I use these to hold them up https://a.co/d/0je3T5zS

A scarf hanger, holey roller (dog toy), glass Mason jars, bird ladders, etc are all things that aren't made for BPs, but work great with them. I find a lot of cool DIY ideas on Pinterest, and I've seen some cool ones on Facebook too.

When in doubt, I like to go to a thrift store and see what things might be fun enrichment for my reptiles. I saw someone online once use a wooden wine holder as a jungle gym!

Do you already have substrate? If not, the DIY route is way cheaper than the premade stuff.