The Epson P800 is $2,407.00 on Amazon today - I believe that it shows that it's a valuable printer (Amazon charges a lot for hard to get items that they have in stock).
The P900 doesn't do ink switching, so you don't lose ink when switching from Photo Black to Matte Black (which you probably do when switching from semi-gloss to matte papers). In my opinion, it is a cheaper build than the P800 - downsized, but not ruggedly built. The ink is also a little more expensive - 82 cents per ml for the P900 vs. 73 cents for the P800.
Tony