Ian, I have just paid around £3,000 including the engineering insurance and had two brokers say stay with your existing insurer (Axa).
I work by myself, 1600sq ft garage (£145,000), and small forecourt, £4,000 stock, 5 vehicles on MID (around £14,000 total value) with myself, my wife and now my son driving for business use, tools, equipment and public liability etc

So, I think you are doing OK compared to mine.

Graham