I think you might have exceeded $300 if Porsche hadn't goodwilled a new dash. Looks like you have one heck of a nice dealer. I would think that replacing springs and a PSE could exceed that as well, even if you went with aftermarket. Or maybe we should overlook they year in which you replaced your clutch. A friend recently paid $3,500 for a clutch on his turbo. Each of these jobs is at least a couple of thousand dollars, almost certainly more, but let's say conservatively around $200/month. This doesn't include tires, brakes, oil changes, or any of the other wear and maintenance items that others have pointed out.

I think a $4,000 budget is prudent. Personally, I spent about 6K on my car last year, including a couple of mods. The year before, I spent almost $25,000 on a rebuild after my engine suffered catastrophic failure. I didn't even consider that in my estimate, although the scepter of major component failure always exists, even if it is not common. Nonetheless,these were real dollars' worth of incurred costs. With a $300/year or /9,000 mile budget, it's easy to be caught with your pants down. For whatever it's worth, I haven't had any maintenance costs in the last three months. I don't think it's realistic to say I now have a zero monthly average cost.

Dancing girls are included, but beer is not.

Among three serial C4S's, I don't recall a year in which I spent more than perhaps $2500.
993, then two 996's. Granted the 997's a different animal: But it seems, not a particularly more expensive one.

All things considered, though: Porsches aren't necessarily the car to buy if you want to minimize your exposure to potentially expensive problems. Most of them are quite reliable for many, many miles. But occasionally, you find yourself holding the short straw. If a 'bad year', when something interesting and important goes bad and costs---what, $5000 maybe?---would put you into financial straits, then it's a luxury best avoided.

Out of curiosity, I just checked Edmonds.com for estimated costs of repairs and maintenance. Over 5 years, on a base 2009 carrera (the earliest year available) it was $18,000. That works out to $3,600 year. I would expect the costs for older models to trend upward. I estimated my costs on an 08 997.1S at 10% higher. I think some of us have been lucky, while some have not. Anecdotal experiences are difficult to draw lessons from, as opposed to the presumably broader database available to places like Edmonds.

Thanks for that info, that puts things in perspective and your absolutely right anecdotal experience is very subjective and shouldn't be generalized.

So on average, it looks like it is a $300/month premium along with the extra gas/insurance + the depreciation on a 2005 model.
From my little research, I think depreciation is a hard thing to calculate after 10 years b/c the mileage/condition plays a big role now. But I think 5K/year is average and then it tapers off when you are at 20-25K price.

$300/month is only a premium to the extent it's more than you'd pay for something else. I've laid out a lot over the past couple of years keeping my daughter's 06 3 series Bimmer running. You're going to incur some costs on any car. I thoroughly went through my own numbers recently for tax purposes. I had no idea I'd spent as much as I did.

The good news is that after the first 3-4 years, the depreciation is very slow, and far better than any other car I've owned. I think you're right on the money with a plateau of $20-25, even with a lot of miles. These cars age very well. As for gas and insurance, I don't find them to be that bad. My insurance premium hardly changed from the 650i my 997 replaced a couple years ago. I also have a teenager, so anything looks good next to that.

Don't be scared off. Theres a reason otherwise-sensible people get theses cars. It's driving nirvana. You may pay a little more, but you get also get more.