I just did my house two months ago, it's a 1928 brick home that had the original single-pane windows.
I used Champion Factory Direct, which has a Factory in Denver and makes vinyl replacement windows, patio doors, and patio rooms.
http://www.championfactorydirect.com/
My house has 19 windows; 10 big ones and 9 little basement ones, and I paid around $11k for a job similar to what MRM is talking about, where they use the existing window frame and drop in a replacement insert, and wrap the outside of the old frame with color-matched aluminum trim, (similar to gutter trim). Inside the house, all you really have to do is clean up, sand a little, and maybe repaint your existing frame.
The windows are vinyl but i'm very happy right now, and I -think- I paid an ok price. The Pella quote for the same job was $24k.
but was not really a good comparison, because it's kind of a different product. But ANYTHING is better than what I had, for sure!
I think I did ok and I would've had to sell a car to afford the $25k scenario, and that's not happenin' right now.
