Also where the hell is your math, 100 times 150 is 15,000! not 1500
...Okay, I am extremely embarrassed at the moment.
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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.
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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.