We've lived here 12 years now. Before us, the original owner lived here for 45 years. The house was builder grade, and nearly all original, when we moved in. Thankfully we had very few actual surprises until this year, but I did find evidence that the original cast iron drain pipe for the kitchen sink had rotted out and was replaced before I took the kitchen down to studs for a planned reno.

All in I think our kitchen was around $20k and that was with me doing all the work other than installing the counters :( I also pulled down a wall, but thankfully didn't need to put in a beam.

We had a minor surprise around 5 years ago: a galvanized pipe that was screwed into the cast iron stack rotted out. I replaced that section with PVC.

This year we had our first real surprise: the cast iron pipes in our basement floor had rotted out pretty badly. That was... not fun to deal with. Break up the slab, find asbestos floor tiles, get 12 years worth of stuff out of the basement to deal with cleanup, etc.