Need some cheap optical filters? Consider theater lighting filters. They even come in wonderful sampling packs!
These are used in the 3D printed microscope described in our Tiny Florescence Microscopy post, and there’s been plenty of people using this trick over the years so your not going into uncharted territory just to save a few dollars. Rosco even has this great website you can use which will give you the transmission spectra of the filter you choose. You’ll notice a little spectra in the bottom right of the app.