My condition inspection costs (by Tom D's definition) zero, other than my time and that of my co-owner.
Scheduled preventive maintenance items due during the same period cost -- oh, I dunno, call it a three-four hundred bucks. Oil, filter, 8 spark plugs, and the carbs needed their 200 hour inspection & parts replacement. Last year was much cheaper; the year before more expensive because a bunch of pricey, limited-life hoses had to be replaced.
Correcting squawks found during the inspection and performing some deferred maintenance -- another 75-ish. We replaced a part that had been incorrectly drilled and installed by the builder and re-rigged the flaperons. It all worked before, but it wasn't right. Now it's right. Will it work? Ask me after the test flight. And we had to replace some cheap but *****-to-get-to parts called out in a SB.
Upgrades and other stuff we decided to do while the airplane was torn apart -- a few hundred more. We tend to defer stuff like that until the annual, which is why we have a track record of having the airplane torn apart way too long. Next year we're starting earlier in the year, and both taking time off work to do it in one shot rather than dragging it out. And now we'll have lights, so that's theoretically another hour a day of legal flying time. Important with winter coming up.