A fair price.

Its always good when someone charges you a fair price and less than you expect.

I once had to call a locksmith because the padlock on my side gate had seized up and could not be opened - not even with WD40. The office woman told me it was a £40 call out fee but it needed doing. The locksmith said it looked like someone had put superglue in it and he would have to cut it off with a grinder. He asked "are you a pensioner" and on receiving the answer, said he would do it for £20 as it was a quick job.

I positioned the new padlock in such a way as to be inaccessible from the other side.

Someone had recommended him on NextDoor app already.

That's a really good price.
Perhaps you could leave him a positive review somewhere, if it would help him?

That sounds very reasonable.