It's not the 2 extra seats, it's the 210. Too many gear up issues in the fleet. Yes, more seats will add cost but the model itself is cursed as far as insurance is concerned.
I pay about $3200/year insurance on my T210F. 4 Seats. The airplane isn't cursed for insurance any more than another high performance retractable is. It's the cost of doing business.
Parts availability and cost are factors. So are the effects of runaway inflation. Number of seats is considered due to potential liabilities. Geography is considered; i've got little chance of hull damage or water damage from hurricanes in Maine. Not so in Florida. Operating from a grass or gravel strip is considered. I don't fly regularly in real mountains. I don't regularly fly with 6K+ DA's. According to my insurance guy, these companies factor in many variables.
The age and experience level of the insured obviously have a great deal to do with insurability in any airplane, but especially in any retractable.
A lot of big, new money without proportional levels of experience has flooded the market recently. The underwriters factor those very wealthy, very low experience pilots flying very expensive airplanes into the mix. Even if they have their own parachutes. Insurance is a risk sharing enterprise.
Sorry, but 250 total hours with a fraction of that in actual IFR over maybe 5 years of flying does not make you an experienced pilot in the eyes of any insurance underwriter. 4 hours average per month is a bare minimum for currency and recency, considering a big chunk of that time would have been dual received chasing some rating or another. So, expect to pay more
Being a young pilot can also work against you, just like being a geezer. I suspect that when I turn 70 I'll have a very hard time finding (or paying for) insurance.
I'm no happier than anyone else here that insurance costs have skyrocketed. Do your homework before you buy. If you can't afford it, don't ***** about it. Don't blame the airframe. Just buy something you can afford.