window replacement; how hard is it?

trying to determine exactly how hard/difficult it is to replace windows. my parents have 5 casement windows they want to replace (1st floor) of a brick veneer split level. 3 are approx 44" wide by 43" tall, 2 are approx 70" wide by 43" tall. they had several different companies come in and give them quotes. the quotes ranged from about $3800 to about $5000 for either andersons or pellas. in getting some quotes for just the windows from home depot and menards, it seems like these companies are charging about 70-90% of the window cost for labor. now it seems like it would be a straight forward thing for the diy'er but the fact that they are charging so much for labor has me thinking that i am underestimating what's involved. can anyone post their experiences? thanks.

btw, regarding my personal skill level, i have done my share of diy projects and think i might be in the above average range.

 

Go to HD or Menards, find the window you want, open the box and read the instructions.

 

Speaking from the contractor stand point, installing the windows is the easy part. Finishing the outside/inside so it looks nice is where the costs come in for the material/experience. I've been called in on many DIY jobs to fix the situation, many times having to totally scrap what the homeowner had started/done just to get back to a good starting point so we coould start in.

Good luck.