Hi, I write in English (Google translator) even if I see that you are Italian,
I bought the mud flaps in a Honda warehouse and unfortunately the price is what you wrote yourself, but where I bought things is a large center where there is everything, car sales, warehouse, mechanical workshop, body shop and I asked for the assembly,
in my opinion they didn't even know about all those operations to be done to mount the splash guards, I left the car with them and went to get a coffee and after 30 minutes I went back to the body shop and the car was ready with the splash guards mounted.
When I asked for the cost they didn't want anything,
they said "for such a simple job" also considering the cost of the accessory.
I think they just drilled the holes and screwed the splash guards directly,
aesthetically they are perfect and do their job,
so i can't tell you what all that stuff about disassembling the bumper cut etc. is for. etc.
Maybe he tries to hear you in the body shop or workshop too, ask him the question, can you mount the mud flaps? and ask how much they want.
Obviously, having also the receipt of the work done with the Honda brand, I am in place with the guarantee