Vinyl Replacement windows for mobile home.

I'm new to this board and have questions about replacing windows in a 1980 Marlette Mobile home located in NE Oklahoma in the Grandlake area. The two I'm wanting to replace for now are slider type. Window opening sizes are 46 3/4"W X 34 3/4"H and 62 3/4"W X 40"H.
I'd like to get descent quality vinyl slider type replacement windows or other types.
Where is a good place to start looking and pricing replacement windows for this mobile home for the DIY'er? Thanks

The first thing you have to do is see how thick the walls are. most replacement windows are about 4" thick. Also, you'll need to probably add in new casings. Other than that, there are a wealth of manufacturers and builders who do mobile homes. DIY is ok, but getting it done by a pro has it's advantages, too. Cost may not be the only thing you should look at, but a correct installation, warranties, etc, too.