If I recall, it was around $700 for the rear derailleur/shifter. Back then a Tour de France bike was only around $3000. The mail order price for a full Dura-Ace STI groupo was around $1300.

I picked up a set of the Zap as a covid project. Other than fixing what the previous owners screwed up, the system actually works pretty well. The only issue I've had was when the battery ran low, it shifted uncontrollably into the smallest cog. It wouldn't let you shift the other way.