It has been said, many times already - each state has different rules/laws and the way we had to do it, in Ohio, was to register the bike with a friend and be a 'named' rider on his insurance. We did this in 2006 - bought an old bike for $1000 and sold it, 5,000 miles later for $900.
The following year, after much research, we found the simplest (if not the cheapest) way was to buy a bike in the UK and have it flown over. It cost $1,800 one way. At that time, it was almost 2 $ to the pound. Now it would be even more expensive.
We then left the bike in storage in Canada. Now, 3 years down the line, we leave the bike with friends and just pay for our flights each year.
That was 27,000 miles ago. We used to tax the bike even though it had never been on the road in the UK, but nowadays (the bike being 3 years old and due it's first MOT) we just use the SORN notice.
So, although, initially it cost a lot, it has worked out OK - but that is because we come over for around 10 weeks each year. If, like us, you fall in love with the USA, then there are many roads to ride yet, so we will be coming back for as long as we are able.
The down side is we don't have a bike in Europe!
You can check out the ups and downs of the whole process of shipping a bike on the website I did in 2007
A Long Ride In America - Home