A while back I looked at buying cutting fluid because using 3in1 oil seemed wasteful and WD40 is expensive. Cutting fluid is pretty cheap but I didn't want to pay for it, so I made some out of vegetable oil, water and detergent to mix the two together. No idea how this compares to the real deal but it is better than air.

Don't think 50/50 is the right ratio, but it is easy enough to invert the bottle and drain off the water from the bottom as the emulsion floats on top of it.