Gen crown needs a gen tube.
Depends on what gen IWC parts you wish to add. Cost for crown and tube you can see via link above. Dial, hands, datewheel etc will add some extra $$$ - if you can source. A fresh ETA 7750 should be about $400, if buying used you might need to add funds for service. If you want a gen IWC movement instead ("7750 based") that should be up to $1000. Note - imo there's nothing wrong with the a7750, given I can use money for something else instead. As always with frankens, there's really no limit to what you can spend - after some time collecting you might realize you've spent more than a used gen costs...