Speaker Sales on Audiogon

I recently listed my Tyler Acoustics for sale with the “buy now option” but had checked the box stating that shipping costs would be assessed after the sale, since I didn’t know how much to charge for shipping because I didn’t know where they’d ship to. I also stated this is my ad.  
Well, a gentleman bought them and he paid me an extra $100 without talking to me about shipping costs, but shipping these to his location is $300 via fed ex...  I sold the speakers at a low price of $699 and can’t justify $300 in shipping.  What do I do?

Also, Is it normally around $50 to sell something on Audiogon?  I paid all of my listing fees upfront ($30) and then Audiogon took another $20 when the item sold as a transaction fee, and on top of that, it looks like I still owe Audiogon $20... 

Oh and to add, I think that next time, I’ll just do a “flat fee” for shipping and I will open a Fed Ex account in order to save on shipping.

I think it may make the transaction smoother if I do a flat fee. For instance, I could have just done a flat rate of $150 for these; I’d take a gamble on whether I’d lose or make an additional $50 but for me, when selling something for $700 + I don’t mind contributing $50 to make a smooth sale happen and end up with a happy buyer and seller!

Jennerl....I tried to contact the shipping company you suggested:
I had trouble getting through to customer service, and when I asked about their shipping service, the phone was disconnected abruptly.

Have you used them?
Here's a tip or two for selling here or on Ebay...don't charge for Paypal as that just seems lame (and anti business) and simply list whatever it is for enough to cover your costs...I estimate shipping to cover "CONUS" only and just have it as a flat shipping/packing fee for simplification regardless of where it's going...if you lose a few bucks or gain a few nobody cares. Over the years UPS has smashed and lost things, as well as FEDEX and USPS so you have to pack stuff well! In the case of UPS losing an amp (A tube Marshall combo amp "disappeared" from a midwest facility), that's what insurance is for...note they didn't refund the shipping fee! Man...