Maybe a bit obscure, but I'll post this in case it's useful to someone.
Some things I learnt recently insuring and registering an unregistered GS 500:
*If you're going to take out comprehensive insurance, do that before you purchase a CTP green slip. In my case, it made a massive difference to the cost of the green slip, like one third off. As I wasn't intending to ride the bike until it was registered, I was going to start with the green slip, but the cost of seemed high (more than my car), so I queried the figure and was told that it was because the bike wasn't yet insured.
*If you are intending only third-party or fire and theft insurance, get a quote for comprehensive as well. In my case, comprehensive was only $40 more per year than third-party, which is well worth paying.