I came across a couple cool artworks and decided to contact the artists to see if I can print them on t-shirts. They both agreed to licensing the artwork and that they want it to be limited. Cool and all... but I have no idea how much to pay for how many shirts.
They both want to work out a deal to where if I want to reprint (print more after my first order) that I will have to pay for it pretty much. Just starting out, I'm not printing thousands at a time, not even 500 yet. I plan to start off with a batch of 200 to test run the design. Realizing all this, I realize that licensing will be much more profitable when I have a fanbase of at least 1,000+. But, I figure, I already asked, so might as well follow through with it.
The first guy, I blindly offered $100 to print 214 shirts. Now if I reprint 3 more times (about 600 shirts), I will have might as well paid for a commissioned design that I have the right to and can print as many times as I want (I usually pay around $300 for those). See how it's not too smart to license at such a small stage? It doesn't seem very smart at all from a business stand point.
The next guy, I haven't replied to yet and it's been about a week, but I'm still trying to figure it out. Is $100 for 500 shirts too little of a payment?
Should I pay per shirt (ex $0.50 a shirt)? I just want an equation or rule or something that I can use for mostly everybody I license from so it won't be a guessing game of how much to offer, you know?
Help

Please.
(Sorry if this is kind of hard to understand, I wrote this at work at the very end of my lunch break so I was rushing!)