Might want to move this to a different section (Digital Goods or CE maybe) since I don't believe the Gambling section should be used for selling stuff, but I could be wrong. Anyway, how much do you have to gamble the 450$ to withdraw it? If the rollover is too high, it probably isn't worth it buying for ~415$. Good luck with sales.
first of all, excuses for posting in the wrong section
to answer your question, I am not sure howmuch should be gambled. I think if you're supernova on their site, you will not have a problem with it, but a couple of years ago I was very active there and once i send a friend some dollars and he told me he couldn't cash out, only after he played he could.
I think the best person to take the offer is one that likes to play poker, this way he or she can play with reduction.