I have 2 X CZ 40Bs
Both I paid under 500 for in the last year.
Having all the information/box helps a lot and like nonamehavei said it all depends on where you sell it.
Also you will need someone to want/know what the CZ 40B is to either pay up for it or at least whatever price you sell it for.
Both of mine where bought from smaller gun stores that really didn't know the story behind them and at the time (pre-corona panic) no one was buying 40S&W - so I got really good deals on both.
There is usually 1-2 CZ 40Bs on Gunbroker from time to time - I watch those and the actual Colt Z40s almost daily.
Is yours a flat slab slide or does it look like it has an indention in it? The indention was actual Colt Z40 rollmarked slides that they ground off and then rollmarked CZ 40B (
or so rumor goes)- Both of mine are flat side so No pre Colt rolled and ground off.
But I have seen CZ 40B and 40P with the 'ground off and restamped slides'
I might pay more for one of those - just for the story. (if it is true

)
Currently the CZ40B and 40P on gunbroker have this on the slides...
https://www.gunbroker.com/item/873846785https://www.gunbroker.com/item/873980154