Relocation allowance for moving O/S?

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I have been a contractor in a company for a few years, and they have wanted me to join them after about a month in. I had never been to interested, but over time I have been a more significant part of their operations they have been making more noise about it, and my later stance was if you make an good enough offer and relocate me to the US, where they are based, I'll think about it. Well an reasonable (but not great) offer is now on the table, so we are talking.
I have asked for a relocation allowance, which I think they have come in low (early days in the negotiation, and they are talking about I would have to pay it back if I leave within 12 months), but want to know what other US companies offer in the real world for people moving from Europe? What is fair and reasonable to expect them to cover? What conditions (for me) should I make sure are in the contract?
There is no OH and/or children to worry about, I currently rent a furnished property, so I don't have a container of household goods. My thoughts are I would put things in storage for 12 months, and see how it all goes.

Thanks in advance

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worsy said:

You need to explain if this is a temp move or do you plan to relocate perm. If temp what is the role going to lead to? Don't forget you will need a visa, most likely will stipulate only that employer too.

Relocate for a permie role. The company is going to sort out the Visa if I agree, but with a E-3 Visa I can move to another company and get a new visa (which isn't my intention, but if the company went belly up for example I have options).

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Thanks Andy and Matt (sent you a PM), it has given me food for thought.

What are the typical clauses for if you leave early? Not that is my intention, but you have cover all bases.