There are a lot of variables that affect maintenance costs. You can look at them as follows:
1. Mileage-related maintenance. For example, if you spend $1200 on four rear tires and two front tires every 10,000 miles, you're paying twelve cents per mile just for tires. If you spend $2500 on a clutch every 50,000 miles, you're paying five cents per mile for clutches.
2. Time-related maintenance. For example, maybe you change your brake fluid every two years, regardless of mileage.
Note that a lot of maintenance can be done based on time OR mileage intervals. Let's take the 30K/60K/etc service (valve adjustment, fluids, and filters), and let's say this costs $1000. If someone is driving a lot of miles, then he's probably doing this service every 30K miles, so that's 3.3 cents per mile for major services, and it's very much mileage-related. However, the interval on this service is 30K miles or 2 years, whichever comes first. If someone is only driving, let's say, 5K miles per year, he might do this every two years, regardless of not hitting the mileage interval, and it's very much time-related. So in this case, $1000 every 10K miles becomes 10 cents per mile for these services.
You can do the same kind of calculations with the replacement of the timing belt, water pump, and cooling system hoses (figure $2000 every 90K miles or 6 years, whichever comes first), oil and filter changes (price depends on the kind of oil you use, the interval depends on your opinion in the endless debate), minor services (coolant and valve adjustments at 45K/75K/etc), etc.
3. Unscheduled repairs. These are things that break or wear out at non-predictable intervals, rather than work that is done on a pre-planned schedule. As long as you're keeping up with scheduled maintenance, these items are largely out of your control.
4. Usage-related repairs. If you take your car to the track, you know that you're going to spend $X to replace front brake pads every 500 track miles, $Y to replace rear brake pads every 700 track miles, $Z to replace front rotors every 1200 track miles, etc. (YMMV.) These costs are the direct result of how you use your car. Your choice.
5. Mods. Entirely within your control and subject to your discretion. You can pay zero dollars on these if you want.
Note that items 1, 2, and 4 are very predictable, based on how many miles you drive over what period of time and how you drive your car. 3 is not predictable but over time, you can budget so many dollars per year based on your usage and if you don't blow an engine, it can be pretty accurate. And 5 is entirely controllable.
Again, Rob's been averaging 8,000 miles per year. Assuming no track usage, typical predictable costs might be as follows, using the calculations above:
12 cents per mile for tires ($1200 every 10K miles)
5 cents per mile for clutches ($2500 every 50K miles)
1.3 cents per mile for oil changes ($50 every 4K miles/6 months)
6.7 cents per mile for major services (30K/60K/etc) ($1000 every 16K miles/2 years)
3.3 cents per mile for minor services (45K/75K/etc) ($500 every 16K miles/2 years)
4.2 cents per mile for timing belt/water pump/cooling hose replacements ($2000 every 48K miles/6 years)
So that gives you a figure of 32.5 cents per mile, based on 8,000 miles driven per year, not including unscheduled repairs.. I think Rob's actual experience of 25 cents per mile is pretty darn low.