It is NOT a Corydorya, rofl.....doesnt even look like one!
To me it looks like it could be a Syno Multipunctatus. Dont think it is a petricola as it does not appear to have the leading edge white tips to its dorsal and pectoral fins and its eye is too big. I have 4 Syno Petricola and it doesnt look like them.
Thats about the going rate for Syno. Multis. what size is your tank? They can grow up to 6", so only get more if your tank is over say 45G. Although you are right, they do prefer to be in groups (3 would be better).