I have driven a 2006 Mazda 3 since 2008... (its about 11 years old now)
Routine maintenance is actually less than other vehicles of the same age.... e.g., oil changes less often, timing belts, etc. We have about 100k miles on it now. The following are typical routine or 'unusual' expenses that cost a bit:
1) The low profile "zoom zoom" factory tires wear out much more quickly than average. I am on my third set. (first set lasted only 35k I think, have maybe 8k on the current set...have put all seasons on after that).
2) Almost no brake work needed, other than very very occasional pad wear. I think this is the least brake work I have ever seen on a car, and we drive our cars for many years before letting them go.
3) Shocks / struts were done a few years ago -- normal age / maintenance cycle.
4) New battery needed last year -- it went 9 years on the factory battery.
5) Thermister needed replacement a few years ago (cheap, but annoying light came on)
6) Headlights now are starting the foggy look, more noticeable recently.
7) New windsheid about a year ago
8) The power windows don't all activate consistently from the drivers side. I have been putting this one off cause I don't know...
9) AC is still on factory original, no recharge or anything...
Other than that, oil changes, wipers and air filters. Oh, and the 2006 is very meh on fuel ecomony especially compared with the new models, but that is not your worry.
Hmmm, Had the spark plugs checked at routine times, but I don't think they have been replaced as yet, at least if they were, it was very cheap so I don't recall.