Costs of sanitary fixtures from different companies compared

Your offer prices for the bathroom items will presumably be the MSRPs.

... or even above that. It has now become common practice for some installers to add another markup.

Especially with concealed fittings, I would make sure to use a reputable manufacturer and not a DIY store brand. In our current apartment, we have Hansgrohe and were able to equip the 30-year-old concealed bodies with new fittings thanks to the still available spare parts. That saved a lot of money and effort. With DIY store goods, often the only option is to chisel them out.

we have the sanitary sample selection coming up soon.

That sounds like a construction project with a general contractor. However, my impression from your thread history—which, by the way, hasn’t exactly been blessed with answered inquiries—is rather that you are about to, or well on your way to, cobbling together a top-notch Wolpertinger street mutt through individual contracts. Google the evil magic word "Regiestunden" (time and material hours), then it will dawn on you why such an undertaking backfires spectacularly. And/or drywall, silicone, acrylic, and expanding foam could unwittingly become the main building materials of your house. The squirrel is not a good role model when it comes to building—but your questioning tactics seem to be made the same way.