Necchis are really nice machines. If a Supernova has been sitting for a while, they are notorious for being stuck. Mine was the "most-stuck" machine I've acquired but with a little work it now runs beautifully. Apparently, the tolerances are so tight with Necchis that they require more frequent oiling than other machines. I know I can hear when my Necchi BU is ready for oil and it quiets down after it gets a drink (but even when it's thristy it's pretty quiet).
First, in looking at the picture, I would want to know if the "lid" is missing from that cabinet as that would be the work surface and wouldn't look as nice closed if it is missing. Otherwise, it's lovely.
I would definitely ask about the motor, accessories and foot controller as they would add to the expense. The motor might still be in it and I'd want to know if it worked. You would not be able to add a different type of motor on the back of the machine as the motor is behind the plate under that handwheel. It's also a tight fight in there and takes an odd belt which is reportedly tricky to change (I haven't had to change mine yet). There are discussions about the belt on the necchisewingmachineclub yahoo group. They also have user's manuals and service manuals for download if you need one.
Sewclassic does have a replacement cord for the Supernova and any foot controller would work.
It should have a box of cams and feet (which are high shank and industrial feet can be used). Here are a couple of examples of what the box and cams look like:
http://www.ebay.com/itm/Vintage-NECC...item232ce52c8b
http://www.ebay.com/itm/Vintage-Necc...item2336d1cfd9
What I found interesting about the cams is that there are some "pre-built" cams for decorative stitches (and a buttonhole stitch) but you can also build other stitches with separate discs. The lid of the box has a wheel that turns and displays the settings and discs needed for different stitches. The nice side of the design is formed by the bobbin thread so you would sew with right side down to get the nicest effect. I wouldn't want to try to treadle one of those designs unless I were used to running marathons. Also be aware that there are different sets of cams, not all fit. There are lists on the yahoo group of which cams fit which series of machines.
How complete the set-up would affect how much I'd be willing to pay. Mine was missing a controller/cord which was easy to replace and a couple of cams were missing. I also got lucky in finding an accessory box in an assorted lot on shopgoodwill which was complete. The cam boxes can be pricey at auction.
Without the cams, you would have a nice zigzag machine. I've seen people report that they love to FMQ on the Supernova, but I can't seem to get my feed dogs to stay dropped (which may be due to operator error).
YMMV
John