The machine looks like a Singer model 15-88. The main giveaway for the model 15 is that the thread tension disc assembly is on the side (rather than the front, laike later machines.) The industrial model 31 machine has the tension discs in the same location bit is about 15cm longer and much heavier.
It's hard to tell the condition from the photos but it appears that this machine has the "sphinx" or "gingerbread" graphics, either one of which makes it just a bit more unusual. If the finish is intact and free of scratches this could be of interest to some collectors.
The price it could command has a lot to do with where you are and what the local market is like.
The main function test is to see if the wheel, with the treadle belt detached, turns. If it turns with little or no resistance it likely doesn't need as much effort to get it in working condition.
One of my machines is a Model 15-90 (with a belt-driven electric motor) from the early 1930s. It's a great machine.
Here are a couple of links with some of the visual details of the model 15 and the numerous "clones" out there.
Cheers and feel free to follow up with any further questions if you like.