I don't know what a fair price would be for that speaker (i forget how much those cost).
But for your protection you need to pay with amazon payments or paypal (NOT as a gift payment). If the speaker arrives damaged or never gets there (and the seller doesn't want to do anything about it) you can file a claim.
Of course, the seller needs to have his own protection too. Take pictures before shipping, package the item securely, and use tracking/delivery confirmation because he doesn't want to send a speaker out to a dishonest person who says it never got there/is damaged.