Until Clarifi, there wasn't any sort of biological or genetic test for autism. Meaning, if you suspected your child of developmental delays, it was up to your pediatrician or family doctor to properly screen and diagnose your child for ASD, based on if they showed typical symptoms of developmental delay. However, this comes with a few complications.
One, symptoms aren't always apparent enough, early enough. If the biggest thing you're noticing regarding developmental delay with your child is that they're not making eye contact with you, you're probably not going to think much of it. So the chances of you bringing it up to your pediatrician at their check up, aren't necessarily high. Then when symptoms do start becoming noticeable, the child is already three, four, possibly even in grade school. They've lost years of potential intervention time before the autism diagnosis process even begins.
Another problematic area comes from pediatricians not wanting to give the definitive diagnosis of autism spectrum disorder. For children with signs of developmental delay, they have to go through several steps in the autism testing process. After being screened for autism by the pediatrician, they could be referred to a professional in child psychology, like a developmental neurologist, for further autism testing. This screening can last a few hours as the developmental specialist tests the child on how they interact and react in certain situations, like play and communication. However, the wait to get an appointment with these specialists can take months to years, depending on how high of a demand vs low of a supply are in your area.
When you break autism testing into just costs, it's not absurdly expensive. The CDC says "A 1998 analysis found that, depending on the instrument, the time for administering a screening tool ranged from about 2 to 15 minutes, and the cost of materials and administration (using an average salary of $50/hour) ranged from $1.19 to $4.60 per visit." To be fair, that's relatively outdated information, but the conclusion can still be made that the cost of a screening via your pediatrician isn't going to break the bank. The real loss in regards to how much autism testing costs is time. And when it comes to intervention, an early diagnosis leads to the best chance of success.
Overall, autism testing isn't much and every parent should have their child screened for developmental delay by their 18 month check up. However, to ensure your child is receiving a quick and reliable autism diagnosis, why not use a test that measure biological components rather than subjective screenings?