How to split to costs?

Hey Glow Community. Need some advice maybe from your own experiences.

I am in the process of renovating my bathroom. The guy who is doing it is a neighbour, we know each other families, our kids go to the same school - super nice people.

Anything I wanted in the bathroom he made it possible so happy with him as a worker as well.

Well the shower tray he recommended ( that is the best) comes in a size that is too big for our bathroom but the supplier said it can be cut to size. So we ordered it but today when he cut it it cracked!

He went out to buy a new one and a special tool to cut it - but it cost him £450

He said I don’t need to cover it.

But I feel like it’s unfair for him to cover this.

I was thinking to go 50-50?

Any thoughts / suggestions ?

Thank you!