Also where the hell is your math, 100 times 150 is 15,000! not 1500
...Okay, I am extremely embarrassed at the moment.
Yes, you're totally right. I have absolutely no idea what the heck I was thinking. Sorry!
Just for the sake of saying something halfway contributory; I think 2500 is probably the best price mentioned so far, with my math skillz now (hopefully) intact.
It shouldn't be an outrageous figure, obviously neither should it be too cheap. 2500 seems like a good balance.
I agree on the no refunds part; however, you cannot have a limitation if you're not going to offer some way to exchange marks in the future. I think if you're going to have a limit of 4 marks, you'll need a refund system (cuts down on the whining, at the very least); if you're going to go limitless, you (obviously) don't need a refund system.