Repair Traverse Rod Cord

I had my house stick built in 1992. I have Anderson Windows in the basement (my house is in northern lower Michigan where we get lots of snow). They were made of soft white pine. The open inward from the bottom. Over the last several years I have painted them with a good latex paint, both inside and out. I also have one of those plastic shields placed over the window well to keep out as much weather as possible. Because these window frames are made of such soft wood, they have rotted out on me in the last couple of years, to the point where I am getting an occasional mouse in the house. I have applied as a temporary fix a gob of that foam spray stuff that dries hard more or less. This seems to have kept both the creatures and weather out for now. My question is this. How difficult is it to replace these windows myself? What should a replacement window cost? What brand would you recommend? I am seeing ads in my local paper saying a guy will install new windows for $295.00. He doesn't specify a brand. And based on ads I see in the Home Depot etc., flyers, it seems these windows won't be inexpensive to buy. I am inclined to do it myself if it is not too difficult. But I need to decide soon before summer runs out. Any suggestions are appreciated. Thanks.

Is there a trick or a tool to remove the plastic operator cover from an Andersen Perma-Shield Casement Operator. I pull as hard as I dare without cracking the plastic. Thanks for any help, Ike