In fact, it is slightly cheaper at AWS.

Ondemand PostgreSQL, Single Node, 1vCPU, 1GB MEM, 10GB Storage is $15 at DO

Ondemand PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $14.29 at AWS (db.t3.micro at us-east-2)

if reserved for 1yr no upfront

Reserved PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $10.57 at AWS (db.t3.micro at us-east-2)

Or you can use ARM and go lower.

Ondemand PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $12.83 at AWS (db.t4g.micro at us-east-2)