Plumbing costs/ Getting a plumber on board

Plumbing is something i know very little about, im Hoping to learn more in the coming months :)
Once we had decided on the method of heating the house, i contacted a few local plumbers one of which was highly recommended i sent him off the drawings and told him in a cover letter that it was going to be oil heating, underfloor to three rooms main bathroom ensuite and kitchen we like the feeling of a hot tile floor!!! What can i say!!! Pressurised system, super condensing boiler located in the garage and 6m2 of solar panels the radiators positioning and quantity were at his discretion with heated towel rails in bathrooms!

He sent me back a detailed quote on the spec and sizes and quantity of all associated plumbing works, i also went to a second plumber recommended by one ofthe other Quantity Surveyors at work he specd the whole set up also and quoted me

The prices returned were:-

Local Guy €21,500
Work Guy €27,500

I decided to go with the work guy as he seemed to spec it better and was supplying everthing with the exception of the sanitary ware he is also experienced at converting to metric for clients who buy there sanitary ware abroad!