It's an early 66-1 or 66-3 back clamper. Notice that the presser foot attaches from the back. Only early 66s used this type of shank. These feet are hard to find and pricey, but you may have a good selection in the accessories box. I think I see a quilting foot and a guide bar, part of the binder, the adjustable hemmer in two pieces (might be fixable), parts of a tucker. I think there's more but I can't see.
A lot of people convert back-clampers to side-clampers by swapping out the presser bar with that from a side-clamping 66. I've seen the parts for sale. Another option is an adapter that screws onto the presser bar mount. If you convert it you can use the readily available side clamping feet and attachments. You're not going to find a back-clamping zig zag attachment or buttonholer -- they don't exist. But if you're not buying the machine for that purpose it doesn't matter.
This machine was originally a treadle or a hand-crank that was electrified. Check out the leather belt! Early! It doesn't seem to have been used much because belts don't last that long. The motor is an original singer, and might be good, or it might not. It's .6 amps, which may be adequate. An aficionado would convert this machine to a hand crank or treadle, as oneday said. Original hand cranks are hard to find but Chinese replicas are available for under $20, and I've heard they work well. (Check out sew-classic) And it's very easy to take the motor off and put a hand crank on. BUT, if you want to convert to hand crank, verify that the motor is attached to a "boss", and not just drilled into the pillar. The hand crank boss is a little protrusion from the pillar that is cast in the metal. I'm pretty sure I see it but I'm not positive. I think Sew-classic has the cords and controller if you want to use this motor. You could also ask her advice on whether to buy a new motor & controller all together or replace the cords and controller. Lately I've been pricing attachments and feet and she has great prices.
The decals are great, but I see some "crazing" and I'm not sure what that means. The machine has been well protected in it's case.
I think a collector who doesn't have a red-eye machine would buy this and convert it to hand-crank, and probably leave it as a back clamper. But that collector has more than one machine.
Keep in mind that any thrift shop machine you buy is going to need some tlc (cleaning, oiling, lubing at the least) because it has probably been sitting unused for decades. It's a bit of a project and not everyone is into it. But the craftsmanship and quality of the old machines doesn't exist today. You can find the threading diagram online and actually try to sew a few stitches, but if the tension discs need polishing it might give you trouble. It's a little hard to tell from the pics if there is corrosion or rust in that area.
Also, I would want to check underneath for rust, but one of the hinge pins has come out of the base, and that needs attention. If you try to tilt the machine back you might damage the wood. The way it is the top will not fit back on the base. It looks like you'll have to carefully put the hinge back into the wood (you'll need two people, I think -- one to hold the machine and the other to fiddle with the hinge) and then figure out how to fix it later.
Wow, am I long winded! In short, I think the value is there. Heck the feet are probably worth the price-- if you just need the straight stitch foot you could sell the rest and possibly get your money back! If you like tinkering and you're up for the project, and are willing to put more money into it for the controller/motor or hand crank, go for it. It doesn't hurt to try to get the price reduced.
--Sheila
PS - Okay, I know I've written a ton already, but I just looked at the pics again and it looks like the presser foot doesn't exactly line up with the feed dogs (in your pic labelled "bobbin"). It could just be the angle of the picture but check that out before you buy. Could be that the foot just needs to be screwed on more tightly. If the presser bar is bent or twisted and it's causing the foot to be crooked, well then you'd definitely want to convert it to a side-clamper, and hope that fixes it.