Diabetic cat and insulin

Ripley, our grand old man, is 17 and has been diabetic for a number of
years. He's on Glargine insulin, 1.5 units in the morning and another
1.5 at night. He's been stable for quite some time. The last couple of
weeks, though, he has been having wild swings in sugar levels: 30 to
400 in the same day.

When he drops into the 30s, he can't walk, vomits, loses bowel and
bladder control. We force feed him Karo syrup or other high-sugar
foods and he comes out of it. Other times, he's over 300, even into
the low 400s. We give him the usual 1.5 units of insulin, because
increasing the dose is a crap shoot and likely to push him into hypo
territory again.

For the most part, he gets a protein diet (chicken is his favorite)
with carbs added as necessary to counteract hypos. Unfortunately, he
has stopped eating on his own and we are force feeding him whenever he
does eat.

Last night, for instance, his sugar level was 33. We gave him a small
dose of Karo but no insulin. This morning, he was 335.

I'm putting off taking him to the vet because that's a minimum $500
and we've already spent thousands on him.

Does this new fluctuation in sugars plus his refusal to eat mean he's
nearing the end? He sleeps a lot, and doesn't seem to be in pain,
except when his sugars go really low.