Figure out the price you want under invoice and tell them what you will pay. If they can't meet the price ask them to please stop calling. If they continue to call, call back and ask for the owner of the company and explain that you don't want any more calls unless you're calling to tell me you're selling to me at this price. Otherwise I will have to file a complaint with the police, the BBB and the State attorney general consumer protection for you harassing me. As the vehicle becomes more plentiful, they will be more willing to drop the price.
Or if they continue, your local TV's consumer protection would probably resolve this for you.
If you really want to be aggressive, you can look them up through your state's business listings and find out where to serve legal notice on them. You then send a letter to them stating every call you make to me you're agreeing to pay me $500. Take pictures of any calls that continue and you can take them to small claims court and get money out of them. Talk to an attorney about proper wording of the letter. This letter may need to served by a process server in your state.
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