While the exact cost will vary, you can expect to pay somewhere between $25 and $50 for a tragus piercing. Call the piercing provider you're considering using and ask, as this allows you to shop around to find the best price.
Piercing enthusiasts generally agree that tragus piercing is something of a specialty, and piercing locations such as kiosks at malls that typically handle traditional lobe piercings may not do them. Your best bet for finding a tragus piercing specialist is to ask at tattoo shops and piercing parlors in your area. Ultimately, it's worth paying a little more for their tragus expertise.