Corey I was a door and window installer for Lowe's for 4 years. Contrary to popular belief (and some of the responses here) window installation can be tricky and there are many variables. I can't tell you how many windows I had to pull out and replaced because they were not installed correctly by another company. If you are looking to go on the cheap Cascade Windows will do fine. A good middle-of-the-road window, and the one I most recommend, would be Milgard.
I don't know how your house is built but if it's stucco don't let someone sell you on the idea of cutting back all the stucco to replace the windows... this adds A TON of unnecessary cost to the job whereas a type of window called a "flush fin" will work in this scenario (the new window slides inside the frame of the old window).
Window labor should start at $100/window and go up from there depending on other factors. Feel free to PM me with any questions.