It seems half inch diameter, 50mm focal length achromatic doublets are not that common; Thorlabs does seem to be the only source, and are (at least at the moment) not in stock.
[1] https://build.openflexure.org/openflexure-microscope/v6.1.5/...
[2] https://build.openflexure.org/openflexure-microscope/v6.1.5/...
I am trying to build a homemade projector, I was looking for what I think is a 'broadband' (visible light) 'non-polarizing' 50:50 beamsplitter but all the beamsplitters I found are quite expensive. Is there a 'lower quality' hobbyist-grade product range of beamsplitters that you could point me to? (Brands or distributors is also fine)
Does the beamsplitter have to be non-polarizing? My understanding is that standard beamsplitters do the splitting by polarizing the incoming light.
Now that I think of it, you're probably using a standard display as your image source? That does indeed produce polarized light. In that case I would try a (common in photography) circular polarizing filter. Rotate the filter to match the display polarization, after that the light will be circularly polarized. I think you could use that in combination with a "standard" polarizing beamsplitter. Depending on the desired dimensions, there are a few available on aliexpress.