There are different ways of doing wetrooms so find out exactly how they’re proposing to waterproof it. Unless your floor is very solid – which is unusual if it’s wooden joists, and very unusual if it’s an older house- stopping a tiled floor cracking at the grout lines is difficult.
Do it properly and it’ll be bone dry half an hour after you finish showering.
Define properly. The UK has a damp climate for a lot of the year which means I don’t think wetrooms work well here – I notice you’re pricing in Euros. In hot dry countries or even properly cold dry winters they can work but in the UK you probably need to overheat the floor with electric underfloor heating to get it dry even with a powerful extractor fan.
Our new house has low temperature underfloor heating and heat recovery ventilation which is humidity controlled – towels will dry in about 6 hours hanging on a rail. Water splashed out of the semi open shower tray takes some hours to disappear. In our old Victorian house the towels wouldn’t dry properly even on a heated rail and the floor would stay wet for ages.