A piss test is like $10-$30 in bulk. DOT and aviation related piss tests for production workers, etc is a bit more comprehensive. A hair test is usually to find the amphetamine abusers, pill addicts, and other things that tend to wash out in 48 hours. Those later ones can get to be from $50 on up into the $300 plus range, depending on how nuts you want to be.
Interns, generally you keep em the hell off the production floor, or at the edges of it so they don't get run over by a forklift. This means less need for a drug test to appease the insurance company, FAA, and whoever else is paranoid about dope fiends making things fall out of the sky that week.
In practical terms, worker fatigue is what results in accidents, deaths related to production defects, etc. But hey, what the hell, just keep making people work 12 hours a day or more for months on end. If an engine falls off, or a tower controller falls asleep, meh, who cares? At least you're pushing production to the bloody limits and enhancing shareholder value!
A pot smoker, he's probably better off doing work on small drones. Someone who's paranoid, and out of it is gonna get murderous glares, and unpleasant reactions from people who sweat caffeine, fatigue, and rage in general. Nobody likes to change their routine to put up with interns, let alone space case interns. If he's lucky, he'll fail the piss test, if he's unlucky, he'll pass it, and the GE workers will kick his ass for doing something stupid.
And god help the twit if he has to do a security background interview, even if it's not FBI/DOD involved. He's gonna piss himself every time the interviewer tries to corner him on an ambiguous answer, which potheads are good at giving because they can't get their shit together. Drunks, tweaks, cokeheads, heroin addicts, pill freaks, they can generally get their shit together for 8-12 hours. Pot heads, they're in a haze, all the time, and for months until after they quit(usually only quitting because they're in jail, military school, deployed in a war zone, etc).
Yeah, they're harmless in terms of violent crime, theft, etc. But on the job site, in a situation where you have to have it together or someone might get killed, mainly the worker themselves, or others around them, no, you can't be in a damned haze.
I dunno, probably just lie and make the sucker think the FBI will come to his house and shove a cattle prod up his ass if he tests positive might be good for laughs. Anything to push him away from aerospace. But I'm biased I suppose.
If I was a bridge welder though, even then I probably wouldn't want him so much as sorting welding rods/wire, because he'd probably find a way to fall off the bridge and become a road pizza while being zoned out.