Hi Hjrdee,
The whole area of site assessment has become a lot more regulated in the recent past. This is as a result of increased threats to the groundwater, for which much of the country (including Sligo) is dependent on for drinking water supply. The list of competent assessors is one way of regulating this.
The quotes that are outlined here might be a little modest in my experience, many assessors are charging approx €700 + Vat, with a further €200 for digger hire.
hope you pass!