Replacing odd-sized windows

I'm dying to remove & replace 'run of the mill' ugly single-pane Al windows in my house.
It's not time-critical so I was planning to do it one by one each weekend. However, sizes of my windows are not multiple of 12 inches....something like 46 1/2" x 58"....therefore I can't just go to HD and purchase one but rather have to order them custom-made.
What's my best alternative at this time?? I'm thinking about going with a whole-glass, double-pane vinyl windows.
Although the project is not time-critical, it's money-critical.
I could spend only $100-$150 per window.
Is there a store that specilizes in odd-sized windows??
Should I take it with a grain of salt and just call a contractor??

Thanks in advance.

 

What is the possibility of enlarging your rough opening to accomodate a standard off-the-shelf replacement window unit? What kind of exterior siding do you have? As long it is not masonry, this should not be too great a task, and if you are doing the work yourself it should be significantly less expensive than made to order windows for non-standard openings.