I think the real question is WHY do you want it.
Do you want to provide a service = Charge
Do you want peace of mind with your purchases and sales products stating all have been tested even include report, included in price (you may add $1 or so on your margin)
If you want to do both I see no reason why you can't.
If people want to pay to have it done fine.
However the question I think you are struggling with is how will it improve your business ? Does the market really need this at the moment etc...
$30,000 / $5.00 even is 6,000 tests just to break even (not including interest etc). If you did 2 a day that is over 8 1/2 years to recoup costs.
Now here is another option that may work and that is testing Nuggets ? Advertise to all of the local Prospector stores that you buy and test these ?
It really boils down to how many tests is realistic, then if there are too many your time is taken away as well. Tough decision.
