Some of the expensive fluids are kinda... expensive.
When examining it it feels like soap (paraffin), glycerin (probably keeps the bubbles from bursting) and some water.
Did I guess it? What do you guys use?
There are many formulas for bubble machine fluid and they do contain some soap or detergents, if you want to make your own you may have to try more than one formula. A solution that works well in an area with high humidity might not work well in an area with low humidity and water quality can also make a difference. Just Google bubble machine juice recipe: https://www.google.com/?gws_rd=ssl#q=bubble+machine+juice+recipe
Fog machines usually use a mix of glycerin and distilled water, usually in a 30/70 or 25/75 mix.