The product cost to actually do an eyelash tint is not very much since you really only need 2 products (the dye and activator) and neither cost over 20 dollors. In addition to that you'll need vaseline, some cotton and Q-tips, all of which should last a long time if you buy in bulk.
Where I live, the dye and activator cost roughly $13 or $14 each. Say thats $30 for the product right? And say you get about 15-20 treatments per tube.
If you charge $10 per treatment you'd be making $150-$200 per tube (minus the $30 product fee).
Therefor, this is a treatment where it's better to charge less, because your clients will be more likely to re-book monthly.
PS: if you work in a salon you can charge 1 to 3 dollars more.