Concrete wall in shower, seamless walls

Hello. We would like to design our shower walls seamless in concrete look. I know there are various providers for this, but the prices are quite steep.

I don't know how expensive such a system is, but I wouldn't experiment in the shower or do it yourself if you're not an expert.

Maybe XXL tiles would be an alternative (then there are fewer joints =D). There are tiles in 120x260 or 100x300 that I've seen, and they usually start at around €150/m². Maybe that would be an alternative... Of course, the installation costs come on top of that.