That search got me about 100 smaller (not 7 inch) monitors, which cost less than $50
Or, you can do your own ebay search, but not in the auto section, search in the regular ebay for:
tft monitor -(7", 7in)
and limit your field to the price range you want. Obviously you can change the search specs to whatever you want, but there are so
many seven inch, and I did NOT want one that big, so I just excluded all those from the search.
Avoid buying one that deals with rear view backup cameras, some have all their images reversed, which makes the text virtually unreadable.