I assume that you mean getting a license plate?
Here in Illinois a simple 2 axel trailer cost less then $20 a year although if may go up in the future as Illinois is having money problems.
Where they get you is when you get a new or new used trailer. Then the fee to issue you a new title varies from $95 to $150 depending on the trailers weight rating. After that first year any trailer like those used by racers will cost no more then $50 per year.