What is the value of a Singer buttonholer model no 160506?

This question can not be answered without additional information or context such as year released, features/functionality or where/when released (ie what region or country).

Buttonholer values can range significantly dependent on a number of factors including rarity and age: from around £49.99 (for basic vintage buttonholers with box etc) right up to several hundred for rare (possibly 1 of a kind/prototype ) models in working condition