It depends ... Vet fees have gone up, like everything else.
Our dog was diagnosed this year with something that could potentially be cured with surgery - otherwise we would have had to have him PTS by now. He had the tests and scans and the op and is a lot happier now. Cost? About £8k I think, and that's because our primary vet shopped around for specialists! He's old enough that our insurance will only pay out 80% of the fees, but still, he now might have 1, 2 or 3 more good years.
We'll have just about got our premiums back that we've paid over his lifetime, but, if he gets something else next year, we'll be covered still (and I have had a dog who got 3 serious things in succession! Wasn't insured - very expensive time).
It's a very personal decision but I think it's important to be think things through carefully. If you haven't PTS a dog before when effective treatment was available but it was over what you could or would afford, you might find it's a lot more upsetting than you expect.
If, OTOH, you have done so before, and were Ok with how everything panned out, then it's reasonable to assume you could do it again.