It depends if you do the claims made or occurance type of policy. If you do occurance then it is expensive from the get go, but generally stays about the same for as long as you have your insurance. This is nice becuase you will always be covered based on when you did the procedure in question, and not based on if you are currently covered by that company. The claims made policy generally is cheaper for the first 2-3 years, but then matches roughly the Occurance policy. The CM policy covers any procedure while you hold the policy, but the second you switch they no longer cover any procedure that you might have done while under their policy. That is when you would need to buy a "tail" to cover you for a specific amount of time. This can typically run 3-4k.
For example, someone gets pissed you didn't diagnose their perio 3 years ago. They sue you. If had an occurance policy, and you are now retired-switched companies whatever, you would still be covered. However if you were under a CM policy and you were no longer under that policy and you didn't purchase the tail, you're screwed.
They basically are similar in the long run, but most people I know do Claims Made because they are poor when they start out.
I'm not an insurance agent, so there might be some variations, I just pay the bills when they come in.