I have a complete set of 4 5x7 Diamond Audio M3 speakers. Originally they were for my explorer, but I never got around to installing them.
I was thinking if I could make them fit in the E, then I could use them, as I don't have money for new speakers at the moment.
Any thoughts on if a 5x7 speaker could possible fit in the factory locations?

It would definately take some modification to make work, but in the front doors I could see that happening, with a dremel, and some fiberglass, and quite a bit of freetime to make it happen. I dont think they would fit into the rear doors though, but I didnt take the time to measure...

Just installed new rear speakers. 5 x 7 definitely won't work in the rear doors unless you destroy/modify the stock covers and attach them somehow to their exterior surface and cover them with the the covers provided with your speakers (if any). Just pop the rear covers off to see what i mean.

When you do get funds, i've found excellent deals at onlinecarstereo.com.... (hope that's okay to say) i got $250 8" speakers for $99.

Not what you wanted to hear (been there), but i hope that helps.