As long as its healthy its worth paying an extra $10 or so dan , you could spend more than that traveling about searching for a Niger cat or in postage etc so I wouldn't see that price a prob as long as its not way over the odds.
Both my nigers are about 8/9" ones slightly fatter than the other I'm not sure if mine hve come from good stock though they should be bigger than this for there age imo im thinking slightly stunted everything else in my tanks grows fine at normal rate