I own a beautiful F-Mezzo. It was the (as my research indicates) second one ever built. It is 100% intact. It has the original case, mouthpiece, ligature, mouthpiece cap, and lyre. Satin Silver plat with gold plate bell interior. It played very beautifully; the sound is like a bass soprano, if such a beast were to exist.
They are very expensive as they are so rare. I would say you can expect to pay well over $4,000 for one in decent condition. Mint examples can go upwards of $5k. The one you mentioned on Ebay is very nice, and is actually just about 50 Serial numbers away from mine! I have never seen that finish on an F-Mez either.
They are loads of fun though!!! I love to play mine!
Steve P