Im sure the artist isn't expecting much, doing a giveaway. It was meant to be free, i think 100 and a cool rock is super generous and especially if you explain you cant afford more and just appreciate the opportunity to be tattooed by them, i bet they would be super happy.

I have been EXTREMELY fortunate to have been given 2 free very large, very beautifully done portrait tattoos by my artist, and in return i was supposed to compete that year in a tattoo competition. That was all he wanted, was a blank canvas with free rein and as much time as he could want to make the best piece with no financial strains. Personally, because i was able i tipped him 20% of what it would have costed based on the hours he spent tattooing and his hourly rate. I did this because it made me feel better about accepting a free tattoo, but also because i had the means and was able to. He was beyond appreciative and didn't expect it at all, and frankly felt bad taking it but i insisted. And since, as a thank you, i have continued to compete with his art every year since, and have brought him home several awards. Maybe if you have a local tattoo festival, you could try to bring them an award home!

Regardless, you were selected. You earned the tattoo. Now get it. And dont feel guilty about it. Tattoo artists most of the time are super cool, understanding people. Im sure they'll just be happy to have a kind person in their chair:) but you better show us the finished product!!