I would echo that - Mollydog is right. The UK guys are just taking a cut. Go direct; aside from cost, the logistics chain is shorter than dealing with a UK company.
Temporary import of a European bike into the USA is as simple as pie. You don't need agents, or - Jeese - brokers. You just take your documents to the customs people at the place of import. Smile. Then they say "Welcome, glad to have you, here's a piece of paper that will let the bike stay six months". They are very polite the US americans.
That's my experience, and haven't heard different from anyone else.
There will be plenty of shipping agents on the east coast that will help you ship your bike back to Europe. Why not start getting quotes from *them* now, rather than the UK, two steps removed people.
My guess would be that you will find a decent deal - it's a common route. Perhaps in a shared container designed for personal effects for example. But that's just a guess - but even at, say, 1000USD, the cost is close to the value of the bike.
btw Count on a long wait if you are shipping your bike from Russia to USA. Think about something to do while waiting. Baha's nice
Around the world 2000-2004, on a 1993 Honda Transalp