It depends on the size of the gem and what you want specified in the report. AGL Charges 55-60 for a gembrief and up to 600 for a prestiege report for stones over 10 carats. Their pricing is here
Is there a way to determine if a stone is natural and/or treated without getting a certification? I purchased a stone that didn't come with a certification, but since I didn't pay much for it, I don't want to incur the cost of the certification. Suggestions?
Well I didn't know this existed till about 10 minutes ago but you can take a look at this link. It is for the Accredited Gemologists Association. You can look up gemologists by your state who are members, that would be a good starting point.
If the stone is still in Asia, I’d send it to AIGS for around $30 or so. If in the USA, then I’d choose the AGL brief for around $55 or so. Another way short of sending the stone to a lab since it is an inexpensive stone is to have a gemologist take a look at it. That said, not all gemologists are equal in skill so you may have to “shop” around.