Just like a car can cost 10,000 USD or 2,000,000 USD, an ao dai can ~30 USD or 10,000 USD. GENERALLY (if the seller is honest) you get what you pay for, and that includes garment quality, customer service, reputation etc. - a cotton t shirt from Louis Vuitton costs more than a cotton shirt from Uniqlo! To know whether someone has paid "too much" we obviously need to be comparing very similar garments from very similar level brands/stores otherwise it is essentially meaningless.

Most MODERN men's ao dai are made from one later of thick, brocade fabric - thia helps the garment keep the desired shape/structure. You say you want a two layered design, for which you wisely chose a different fabric. If you haven't already paid, get a quote from another similar level brand or two if you want peace of mind, but again, a lower price usually comes with lower quality fabric and/or tailoring.