The description is a bit vague and likely to be misunderstood. You don't mention if planning is needed, or if there are plans for the extension.
Is the extension downstairs? What is to be contained in the extension or what is its purpose.
Are you renovating the upstairs or converting the space into a bedroom and bathroom?
I would suggest posting a detail description of what you would like to do on one of the onlinetradesmen.com or tradesmen.ie type sites.
You may get a better indication of budgets from a variety of sources that way. Also the better your project brief the more accurate the cost estimates.