How would you convince a domain owner to sell his domain to you?

I'm wanting to have a domain name for my business that has already been registered by someone but that he is not using. He is offering it to me for $1000 (which is too much for me) and I offered him the sum of $300, which he is not interested in. How do I convince him to sell me the domain for a lesser price?

As per my findings, that name is also occupied at social media sites, and the .org domain name is also occupied.

Edit

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This is what I am planning to write to him:-

After a long thought, I have reconsidered the offer for you for this
domain. I understand your expectations. I can pay you something like
500USDs as compensation and I think it is a fair now. There has been
sale of similar domains around this price range. And this name is
already occupied at several social media sites too & other domain
extensions are also occupied so the things are not that easy with
this. I have stretched it out beyond the maximum I could pay for any
domain. This is my last attempt to negotiate for this deal, with my
best offer, as I think it might be offending you to take this further.

I would request you to give your approval now to make this deal
successful.

Give it a thought and let me know..

Edit 2:

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After having sent him an offer for 500$ 3 days ago, I have just received back a response from him, after 3 days, saying "750$ & its yours! " but I just completed the purchase of another domain for 400$, a few hours ago :(. Now his email that could have filled me with joy is now not making me happy because I have already paid from my budget. Assuming I am still interested in this domain but not at the price that I put previously(500$), how should I take this further? I can now only pay 200$(& that already makes me overbudget) for buying this another name.

He is offering the domain to you for $1,000 and you have offered him $300, and thus we know the current value of the domain is somewhere between $1,000 and $300. So you have several options:

1. You can negotiate with him to see if you can find a price that is agreeable to both of you. In the US, watch a number of episodes of Pawn Stars to get a feel for price negotiations (haggling).
2. Make an offer, then wait some period of time and see if he is willing to lower his price. Of course the value of the domain could stay the same or go up (or be sold to someone else).
3. Tell him your absolute maximum price and if he won't agree to it, move on to a different domain name.
4. See if he is willing to take money and something else in barter for the domain name.

Don't say "something like 500USD", give a specific price, as you want to avoid going around in circles.

Really you will reach the stage where you give your final offer and you're prepared to walk away.

Gary E gives some good options, so +1.

The seller split the difference between your $500 offer and his $1000 asking price. A common practice in US style negotiations. But with the purchase of the other domain and the reduction in your budget you will probably not be able to complete the transaction at this time. Depending on how badly you want the domain name and if you are still willing to spend the $500 you might be able to negotiate a purchase over time. If I were in your shoes I would try this: "Thank you for responding to my inquiry. I appreciate it. However, While I was waiting for your response I found and purchased another domain. Unfortunately, that means I now have only $200 left in my domain name budget. I would still like to purchase your domain but I will need to make the purchase on a payment plan and $500 is my best offer. If you are interested let me know and we can work out the details - say $200 now and $100 per month for the next three months. If not, no worries. Thanks you very much for getting back to me. Best Regards, ..." Anyway, that's how I'd do it. :-)

I also believe your best shot would be to just put your offer on the table, but then act as the deal is already made! "Lets do this" "Im ready, are you?" if he is still negative, then let him know you are done with negotiating and give him a deadline! If no response then you really need to move on... He is always go back and regret it;)