Painting, varnishing, or replacing wooden windows and interior doors?

For interior doors, you can also consider applying a film. There are films that also imitate wood patterns. We have something like that in white in the basement. Otherwise, we replace everything. I would also not only change the color, but maybe also replace the damping plastics or silicones or whatever that is. Our old doors and windows liked to slam shut.

The community around the colors of "Miss Pompadour"

Chalk paint is the magic word ;) I once had it for a piece of furniture, was not satisfied with another brand. But I would also test the Miss P brand again.

I would have it done. If you really want it clean and durable, it takes quite a few hours of work per door and window. Remove all fittings, degrease, sand, degrease, prime, sand, fill, sand, paint, sand, paint… That might be fun for two or three doors, but with 10 it's torture. With windows it's even less fun because you have to clean everything, every recess, every groove extremely well beforehand. You also have to replace the seals and rubbers if you want it to look nice, otherwise you end up with dark brown frames that stand out a lot. A craftsman can also achieve much better results with spray painting. Chalk paints? Never again. They looked too smeared to me.

Oh, you mean the price from a professional?! No, I can't tell you.
Let me put it this way: whoever has it done has too much money. If, of course, you have everything done (including walls), then just ask for a flat rate.
If you can't paint, then don't do it. It will be noticeable.

As I said: I misunderstood your question. Many people aim exactly to save money - every hundred bucks hurts when you have to pay for something you can do yourself.

We are modernizing/renovating the whole house. Sure, I want to save something, but I weigh what I can do myself and what only looks good if done properly.
Or just buy new, no idea how much a new interior door including frame costs?!
Is the added value of a new “simple” door big, or is it just appearance?

We painted half of our apartment with chalk paints and are thrilled with the color. All our door frames have become anthracite, and we bought the door leaves new in white because they were really worn out. The difference is astonishing.
However, the whole thing required 4 coats of paint. Stainblock once, anthracite twice, and a topcoat so that nothing causes any more damage.

With the white shades, even one more coat might be necessary, as they don’t cover as well.

We did the frames on the side, one coat in the evening or so.
Costs are manageable, I think around €200 for 10 door frames.

The old frames were brown and didn’t look good anymore. I will look for a picture

We painted half of our apartment with chalk paint and are enthusiastic about the color. All our door frames became anthracite, we bought the door leaves new in white because they were really worn out. The difference is amazing. However, the whole thing took 4 coats. Stainblock once, anthracite twice, and a topcoat so that nothing causes any more damage. With the white tones, even one more coat may be necessary because they don’t cover as well. We did the door frames casually, one coat in the evening or so. Costs are manageable, I think around 200 € for 10 door frames. The old door frames were brown and didn’t look good anymore. I’ll look for a picture

That sounds good! Why chalk paint specifically? Which ones and where did you get the paints from? Did you sand beforehand and then prime (is that the Stainblock)?