I used Humphrey's out of Kansas and had them build it custom to my specifications, which was 4' wide, 3' tall. They made the window and the outside shutter. If you go that route, consider how these two will be installed together, as in, how the framing will be set up. Luckily, I had a creative and inexpensive welder guy to use to help me install it into my truck.
I think Sonny raises a good point about the durability of household windows. But I have seen lots of them used in other trucks and carts. I think ultimately, you will have to determine whether you want to go the cheaper route, or the more "pro" route. On the plus side, household windows are pretty common and easy to replace.