Translation:This sweater is not cheap.
Sweater is British? Colour me surprised, never heard anyone refer to it as that over here, always thought it was American.
In Japanese does this imply that the sweater is not of poor quality? Or would it only be about the price?
Cos these would modify plural nouns and this modifies a singular noun. So, this sweater, these sweaterS.
First, the adjective is やすい, not *やそい. Secondly, this is how you negate an i-adjective; the negative of やすい is やすくない.