On the contrary it can be very cheap if you know what to get. I would go GH flora series micro and bloom. 1 liter bottles if you are strapped for cash. They are around 20 bucks each. And follow the lucas formula (https://www.rollitup.org/hydroponics-aeroponics/4387-lucas-formula.html). Its is bar none one of the best formulas I have used. Check my grow if you wanna see how good it works. And if you go synthetic with the lucas formula it would be a good idea to use h202 (hydrogen peroxide) you can get the 3% solution at your local drug store for 2 bucks. I usually go 1 cap per gallon and it does wonders by adding an extra oxygen molecule to your water. Any more questions hit me up. []Deace!
Pee is actually an all round good nute. But the amounts of certain nutes in urine depends on your diet. Its a risky way of doing things. Hey if your gonna use urine you might as well look into night soil!! haha =P