I don't see any need to 'track' costco gas prices in my area, because at least in western washington state, my local costco is always the least expensive option for regular unleaded. My choice of whether I go there to fill up is simply if it happens to be on the way to/from somewhere else I'm going or is not an unreasonable detour. Or I need to do some other costco shopping. Or it's late at night and the costco is closed, so I have to go to a 24x7 place like an ARCO.

The gas price savings easily pays for the annnual standard costco membership.