My house uses Andersen casement windows. The weather strip is kind of old and very stiff. Also I think it causes the window hard to open/close. Where can I buy those weather strips? If I hire professional contractor, how much would it cost for replacing weather strip per window (total around 25 20x55 windows)?

I have a 1950's era house with only 2 windows in the basement. We had new vinyl windows installed 5 years ago and did the 2 basement ones. I was thinking of adding another window at the front of the house or the side. The problem is the front of the house has brick 1/2 way up , to the base of the big front window. I would need to cut through the concrete foundation to add windows. The side does not have brick, but it is on the shaded side of the house. If I hire a contractor I want to make sure I know what is involved. I can do it myself, even though this not really my area of expertise. How difficult and potentially expensive is this project?