Power cables – alternative hardware store?

night, I was yesterday biting through the shops and fell out backwards at the cable prices. 8€ for a meter 35mm2 I find quite violent.Hads then let it be and looked at ebay. then a buddy told me that one could theoretically also take stink normal power cable out of the construction market. certainly in similar strength (will have 35ers) and well isolated. might be a lot cheaper. in my eyes is current and if the cable I’m surprised that I haven’t heard anything about any of you doing this… what do you think about it?