First, whoever contacted you is in violation of eBay policy, so your first decision has to be if you want to deal with someone who would do that.
Assuming you are willing to take that risk, then unless the person is presently the high bidder and that is the amount you are willing to take, you will have to cancel all bids, then end the auction early, then relist with an opening bid equal to the amount offered.
I see you are a new seller, you should know that such offers are often made by unscrupulous buyers who figure a new seller will often panic and grab the first halfway decent price they see rather than wait until the end of the auction when often most of the bidding action takes place.
This person will probably tell you just to send them a paypal invoice and they will pay it, which they likely will. What the will not tell you is that in addition to violating ebay policy you will no longer have ebay buyer protection, if they later cancel the paypal payment or file with their credit card company they will end up with both the merchandise and the money, there wil be nothing you can do about it.
Wish my fingers would pay closer attention to what I spell correctly.
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