500g is far to heavy for one pony, I would politely say that you are unwilling to pay more than the amount quoted by royal mail (LadyG's link). They are obviously trying to take you for a ride. Is this eBay?

I was just quoted 7.24 GBP for shipping one pony, I have a feeling this is about the same seller and auction. (from uk to my country is usually about 2 GBP)
Seller has kind of quirky feedback, right? And gives very short replies, very few words? If so it's probably the same one.

Also, about another auction, I was quoted 7 GBP for shipping one pony. That seller specified it as Airsure though.

Personally, I don't think this seller is willing to be reasonable at all. If you could get the pony from some other seller, I'd recommend that. This person may just be more hassle than it's worth.

It does sound like it may be more hassle than it's worth What are their UK postal prices like?

Wow.. if you do send it to someone in the UK I would ask for a quote for that too, he might try and charge you 9GBP for that!!

wow I dont think that seller sounds very reasonable at all ! there is absolutely no way that one pony weighs anywhere near 500g anways!. I've weighed (and posted) an adult G1 in a thick small box and it only came to 200gmax weight or less! It only cost me £4.30 i think or very near that to send 2 adult G1's giftwrapped and boxed from me in the UK to an Australian buyer today

a 500g pony!? LOL i have gotten ponies shipped from the uk to myself here in the us and has cost not near that price. i had a fairly large box that had 7 or 8 G1 ponies in it that only cost about 8 or 9. does he think your dumb? i would notify Ebay of shipping price gouging, if this is taking place on ebay.