I only need them occasionally so do I spend $300 for a pair from Volvo or can I get a decent wire pair from the auto parts store?

It's recommendable but not compulsory. Volvo just wants to make a few extra bucks. Buy decent but less expensive ones on the open market.

Nope, just run down to your local auto parts store!

I agree with the other two answers before mine. Volvo is recommending their chains but that's advertising.

No it is not a necessity. If your area requires the use of snow chains on top of snow tires then use which ever you prefer. Volvo will sell those items to make extra income. They do not have any properties which make them any better then a standard snow chain. Hope this helps.

no