Not the OP but I just got done with a codebase-wide re-architecture (driven by a need for a complex data migration) in a little ~2.5 weeks. 800+ files changed, 60k+ line diff.

Without AI it would have taken me several months, and that is only if I managed to avoid burnout. The vendor quotes we got just to see if we could outsource the work were all six figures.

Ya migrated about 50% of a code base to a new architecture from a legacy architecture. I've seen a massive speed improvement in my app since doing this and significantly less bugs. The code base is probably on the order of 150,000 lines of code or so. This refactor took about a week with AI... this would have taken easily a month or more if I did this myself. I also had AI write me a bunch of tests that never before existed in this codebase. Obviously these tests aren't perfect, but neither would mine be if I wrote them by hand.