That seems a tad pricey, but not outrageously so. Syno prices seem to vary quite a bit depending on whether someone breeds them locally, how 'exotic' the LFS's stock usually is, etc.
One caution: a single petricola will not be a very happy or amusing petricola. These fish do best in groups of three or more. When kept that way, they are very social and playful and will freely swim about. Kept by themselves, you're much more likely to have a recluse that you rarely see. That's not a guarantee, but much more likely when you keep them as singles.
You might want to look into purchasing some online... even with delivery, you might be able to get several for less $$ than you expect.
HTH,
Jim