I'm in a similar place, with a P800 and considering the economies of working with roll paper. I can say if you are considering working with canvas, don't bother with a Logan mat cutter, a new blade lasted about 4 cuts before it wouldn't cut cleanly any more. Even on the second cut of Epson Water Resistant Matte canvas, it frayed at the tail end of the canvas, and most cuts thereafter. Instead I've invested in both a 18" t-square and a 16" x 24" roofers square, and will try working with an accurate 90 degtree line and a hobby knife. Don't get me wrong, I'd love a rotary cutter, but don't have space for yet another large board. If you're competent with a hobby knife, it should be okay. When I do eventually get one, it'll most likely be a Rotatrim MasterCut MCA2, single square bare, or the Professional M24 with twin bars.
My other reasoning was, if you should print off a panorama which doesn't utilize the full 17" width of the paper, you're still going to have to use the hobby knife on the longer side anyway.
Regarding the D-Rolller, there are a few videos out there showing home made equivalents. I'd build myself a good one.