Am I really saving money?

Comments I read elsewhere on a article about membership club shopping (i.e. Sams, Costco) got me to thinking about how I spend my money on groceries.

Living out here in the country (or rather, in a rural area, since I do live within the "city limits" of my town), I basically have 3 options for buying stuff; depending on what I need and when I need it. The first is local shops. Now, like many small towns, I'm limited in selection here; especially with the closing of the local general/small department store. In fact, shopping local for me is pretty much groceries (which I include the butcher and the farmers market), auto parts, prescription drugs and specialty items.
The second option is driving into the bigger cities; in theory, that's a choice between about 35 miles or about 130. In practice, I can get from my front door to the shops in Dodge City and back in 75 miles, which makes travel time about an 1:10 (or 1.15 hrs). Figuring gas cost at $3.50 (a little cheaper than what it is right now; but about I was paying a month ago), and a slightly generous 30 mpg (highway my car usually gets about 29.6), that's $7.50. Since I get oil changes free for the life of the car at the dealer I bought it at, I'm not going to worry about that portion, nor am I going to figure tire life into it. I will figure in my drive time, at a modest $15/hour. Feel free to change that for your own calculations, depending on your pay rate and how much you value your time away from work. That brings the cost of my trip to $24.50 to make a run to Dodge. To get to Wichita, it's a little more than $90.
But what do the numbers actually mean? That's the difference I have to get to in what I spend there and what I would have spent here -- or spend on items that are not available in town -- to be able to say "I saved money." If I don't have a cost savings of $25, then I would actually be saving money by spending a little extra at home.
The third option is shopping online. Unfortunately, outside of a few specialty foods companies whose ads we've all seen one place or another; grocery delivery for me is out of the question. If I was in a bigger city where such a service was offered, then I might consider it. Much like travel time when shopping out of town, the difference between buying locally and online is in the shipping (working with the assumption I would spend the same amount of time "shopping" for a particular item). Is a particular item different enough from local offerings or the savings on the total order great enough to cover the cost of shipping? The first is subjective, but the second is firmly objective.
Does this mean you should always shop at home? No. But it does mean that in small communities, you should work with the local businesses to make sure they know what the types of goods you have to go out of town for; and what they could be carrying to make sure your money goes to them.