I got one really cheap at www.enginesonlineshop.com
and even though they said it's legal, I think in my city it's not. I got a ticket from the police to register with my local dmv. When I went down, they made me buy a $50 permit for my 2 stroke bike. It's good for the lifetime of the bike. It's just a way for them to make money. Anyways it is legal to ride but you must pay the $50 permit. Which evens out since the kit cost me only $150 on the site with free shipping.