I think you will find that insuring an older car is always going to be a lot more expensive because the likelihood of you making a claim is going to be higher than if you had a younger cat.
From personal experience, it is better to be insured than not. My previous cat, Mittens was insured via a company policy up til 2001 when my husband worked for Enron. After the company went bust, we contacted the pet insurers to offer to pay for the insurance privately only to discover that the insurance premiums that had been deducted fromy my husband's salary for the past 12 months had never made it to the insurer's
so the policy was already well and truly void. We were unable to insure Mittens with any company from that point on also because by then, she was 11 years old
In her final year, we paid in excess of Â£5000 in vet fees to treat her diabetes and for ultrasounds, urine and bloodwork when she was diagnosed with cancer. Now, even if we had been able to find a company willing to insure her aged 11 years and we had to pay Â£10 per month in premiums, we would still have been better off financially. We were lucky in that we were able to afford Mittens' treatment and even with the benefit of hindsight, if we had to do this all over again, we would still have paid for the treatment because she had a good quality of life until the end.