A core developer of Django, I think Carlton Gibson but can't find it, mentioned in a podcast that if one were to commission the development of Django's admin interface from scratch today, it could cost around $1 million USD.
The admin has a a LOT of features.
More importantly, it's been continuously evolving for nearly 20 years at this point.
Anyone who's actually tried to do a from-scratch rewrite of a system that has 20 years of development behind it will know that 5 engineers for a year is probably optimistic!
200k/year might sound like a lot but then in a real business there are various overhead costs as well.
I'd say $1m is probably on the lower side of the estimate. Factoring in project delays and misc Murphy law things, wouldn't be surprised if a mediocre team underdelivers with a crappy immitation of the django admin interface after blowing through a couple mil.
Add on top of that documentation, testing, and making the whole thing completely independent and pluggable (as django must work without it) but perfectly integrated with it (settings, forms, template overrides, etc).
That's a lot.
You might get feature parity with less, but not with the same guarantees of stability and maturity.