Thank goodness I don't live in London like @Jameszy having to pay 1.3k for insurance.
I bought the 2.5 last year to add to the Z3 we have and shopped around for insurance ended up going with Lancaster for £183 Fully Comp no extras which was the best I could find. One year on got an invite to renew at £183.90, studied the paperwork and saw that they include an arrangement fee of £49 in that price. Went on all the well known comparison sites and they came back with many options, Lancaster the cheapest on each site but at differing prices based on same info entered, found Confused.com came back with a bargain £125 Fully Comp. I was intending to phone their renewals and ask why the massive difference from their renewal price and new business via Confused.com, however the phone rang a short while later and it was Lancaster asking if I was interested in the £125 quote I had on Confused.com. I quickly pointed out I was an exhisting customer and the renewal I had received was well in excess of what was quoted on confused.com. I was extreamly interested in taking up the £125 quote, answered a few questions and duly paid the premium at £125, documents followed via email within a short time.
I would add that I did enquire with Chris Knott Insurance who is on this forum but they could only offer insurance around the £200 mark so that was a dead end for me.
Currently age 67 and 1 year NCD on the Z4, living in South Wales, limited mileage of 3k annually.
Always pays to do your homework before taking out insurance certainly did this year for me.