Local ultrasound places normally do gender packages as early as 15 weeks starting at $99. If you find out later in your pregnancy they were wrong they will refund you and give you another ultrasound for free! The one in my area is tiny toes
I would not do it before 20 weeks!! By week 20 baby is completely developed to know if it's a boy or girl!! I know a lot of girls that have went in 14 to 17 weeks told what they are having and was wrong because they weren't developed enough!!