My First Beamsplitter

Ordered and arrived two days later - a 50R/50T Non-Polarizing plate beamsplitter from Edmund Optics at £29.75 each I think it's one of the cheapest things they sell.

The beamsplitter does what the name suggests reflecting some light and allowing the rest to pass through. They come in different ratios and mine is 50R (% Reflect) / 50T (% Transmit). The ratio is specified at a particular angle of incidence and wavelength so it's good to check for your specific setup. But as I'm going to be at the defined 45 degrees it's all good.

Here you can see I donned blue latex for the occasion, not wanting to immediately destroy it with my dirty mitts. How I might mount it is a completely different question but have seen some cheap slide clamps that might do the trick.

Fig 2. 50R/50T plate beamsplitter

I was looking at cube splitters also but they are starting at £120 so I thought I would go cheap while still avoiding ebay at the same time. 

If you want a free one and have a dead CD-ROM / DVD-R drive you can recover a tiny 3mm square one however I have no idea of their properties but have a few kicking around.