As they say if a deal is too good to be true, it probably is.
You don't say what avast version it is for but even if this were for Avast Pro the cheapest of the avast products, this would be more than 1usd for a single year.
If it isn't from Avast directly or from an Authorised Avast Reseller I would have my doubts on its authenticity. But without more detailed information no one could investigate it fully.
