Do I feel I am paying too much? Don't know. But it is always a hassle trying to find the money. So yes, the premium is very high.
When a lawyer calls do I have enough coverage? Who knows. I asked once how to determine what would be an appropriate amount of coverage, given the nature of my work. The insurance company told me to carry the minimum, that way I would not become a major target in a lawsuit. When lawyers gather to discuss commencing an action, the FIRST item on the agenda is "Who has the deepest pockets?"
What deductible amount should you select? It's your choice, and your decision.
Can you get coverage on a per job basis? Yes, but you'd better check with your particular insurance company.
If you are a one man firm what do you do? I am a one man firm and I pay, pay, pay. You must build it into your overhead. That's one reason why engineers must charge $100 per hour. (My rate is less than this.) Another note concerning one-man operations: I cannot prove this, but I believe the insurance companies frown upon such operations. The first reason: who is checking your work? The second reason: Many expensive lawsuits are the result of one-man or small operations. (Expensive in relation to the premium which they can extract from such firms.) So the insurance companies do not want to encourage any engineer to hang out his shingle.
Have I had any luck with clients signing a limit-of-liability clause. Nope. I've never heard of such a thing. In some places, you can operate without insurance as long as you tell your client (in writing) that you have no insurance. Then he has to say (in writing) I understand you have no insurance and I authorize you to proceed. It is my personal opinion this avenue is for numbskulls.