I replaced the back two door speakers in my 96 850, they're really easy to replace and I got two for 57ish really good alpine SPS-130A its as simple as snapping off the speaker cover taking the screws out. you'll need to make new holes in the plastic surrounding the speaker whole just aligne the speaker as best as posible. there are two wires in the back of the speaker and its not a problem if you swap them, but it's pretty simple there's a big (wide) one and a skinny one and they go on the corresponding connector. you don't need any of the existing hardware; the old speaker, the plastic casing that covers the speaker, the screws, and the clips ( I don't think they work with those speakers).
I wouldn't go with the speakers from a junk yard they'd be really risky, you never know what quality they are in. I think your best bet for speakers would be new.