Sourcing crystal o-ring

[drop]

I'm told the appropriate part number for a 1665 crystal o-ring is 29-317-8 but I'm having trouble sourcing one for a resonable price (i.e. >$20 for a silly piece of rubber).

Any advice, perhaps a cheap alternative?

Thanks.

[dieselpower]

I bought an O ring from a Cousins watch parts in the UK. They have loads of different sizes. Hope this helps.