I've been given a decent quality bandsaw with a broken plastic top wheel.
It's had a hard life (at a small company) and the tyres are shot... The
motor, fence and basic frame are fine though.

The manufacturer wants £100+ for a new wheel without the tyre. I'm hoping
I could DIY it for a lot less than that.

I've seen suggestions to just layer up some ply, use a circle cutter jig
on my tablesaw or router table then fit a tyre and balance it - but I'm
wary of fitting the bearings successfully into the centre.

Is there a better way to do it? Are there any good UK suppliers for
bandsaw wheels and/or tyres, or a recommended DIY approach to making them?

The wheels are 12" diameter, tyres are about an inch wide, should be
~1/4" thick.