I made stuff out of thrifted curtains! And spirit halloween has over 50% discount after Halloween so I got a bunch of their black spider web things. I painted my dressers and desks (thrifted) and I also just collect larger poster things over time, these rooms are built not put up in a day. You can also usually find somewhere to print posters for cheap or print out like 200 photos for $20 on Shutterfly