It's fun to make your own stuff, and by doing so you know exactly what is in there. I do use preshave oils sometimes, mostly in the winter when the air gets rather dry, but I only use a few drops of it. I did make my own, but any savings were not noticeable for me - I made a 2 oz bottle and it is still near half full, over a year later
Aftershave splashes, on the other hand