Window replacement cost for Duplex - need advise

[Zoran Domazet]

Hey guys! 

I wanted to get some advise regarding replacing my windows in 1 side of the Duplex. The other side has been upgraded a few years back with single hung vinyl windows. I am currently shopping for estimates and so far the lowest quote I've received will run me $500 per window (window, installation, permits, disposal of old windows, and seal around the trim). The unit has 5 windows on the first floor and 5 on the second floor. The windows that I've received quotes are for Jeld-Wen 35.5 in x 53.5 in V-2500 Series White Vynyl single hung windows, which run between $260-280 per window. I found windows in my size at Lowe's for $145 per window, I am wondering if this is something that I can do over a period of a week or so. How difficult are windows to install on a concrete/masonry block house or should I keep shopping for quotes? I feel like the quotes I received are somewhat high. Let me know what you guys think.