If real urine is better and works 100% of the time, then why does the synthetic stuff cost more.
What makes you think this? Real urine is not always better. With real urine, you have to be really sure that the person youve got it from is indeed drug-free (that includes scripted and OTC meds to avoid hassles from the MRO). Plus you have to be sure that the person has not drank a bunch of fluids prior to giving you the sample for sub (which can lead to a "too-dilute" test result).

Human urine also has a shorter shelf life than synthetic. Synthetic urines can be stored at room temp for much longer periods of time (up to 2 years) than human urine.

And as far as cost goes, theres online vendors that sell dehydrated urine at a higher price than most synthetics on the market.