The rationale for this is to have a sink for all the different kinds of string that may be cropping up in your cupboards at different technology levels (taproot/fibres/hide straps). The curio should be rather at the low end of the curio range. In my suggestion below, I may have made it rather too good (half the amount of LP compared to a primitive doll, with equal amount of study time and attention. Maybe increase the material cost to one rope, and increase the study time significantly (I just did not have the heart to put it at levels with the terrible Leather Ball, even though the materials for this one is easier to come by than those of the ball.).
Arbitrary balance suggestion:
Materials: 4 string (or 1 rope + 2 string)
Base LP: 250
Study time: 8 hours
Attention: 4
Inventory space: 1x1 tiles