Most devs will say less, but the reality is most of the time you build the wrong thing first, and the price you quote almost never gets what the client wants/expects and includes many overruns.

Every single contractor will say: that never happens when I do it...

This is a better solution for many businesses.

One, they already have a steaming pile of crap that kind of works. Forking that over to someone to "fix" for €10-50k is a steal - even if there's a decent chance they deliver nothing valuable.

You're talking about on the low end a few weeks of a dev's salary. You get next to nothing for that most of the time...

You could easily spend 4-5x that, take 3-4x longer and get something you can't use at all.

Happens all the time.

As some already said; the real win is into having a business driven prototype; the work to gather those specs is already done and, generally, very costly when done in the traditional way. So from scratch if having to do all of it is more expensive; technical from scratch far less so.