For a decent electric rifle in that price range, you will almost certainly be buying a Chinese copy of a Japanese or Taiwanese AEG.
If that's ok with you, and you want all the things listed, I would most likely get an Echo1 brand gun, which uses a plastic receiver but does come with a warranty and is decent as far as the Chinese guns go.
How's this look to you? You can also get a sidefolder version, or one that has a non-ris forend but uses a detachable carry handle, which you wanted, rather than a flipup sight.
If you are willing to buy from overseas you can get one with a metal receiver, but you're out of luck if it arrives broken.
Personally I would just settle for a pistol or other type of gun or go a little higher in price, but this is, I realize, for an 8 yr old.