What should I tip?

I’m getting a tattoo that is going to be about $300-$400 (3-4 hours of work). I was planning on tipping $50... but I’m so tight on cash rn im giving it second thoughts and maybe doing $25... A few people have said that $400 is expensive enough and I don’t need to tip?

What do you guys think...

EDIT: thanks guys, I have a $50 bill but I’m going to stop and get another $20 for a $70 tip