Hi there,
First thing to do with the Apisto nijsseni is find out if they are wild or captive bred.
If wild, then you're looking at soft water and acidic conditions (and if tank bred whatever the water conditions they were bred in, which could be anything from acidic to alkaline and soft to hard!!!).
They are part of the 'Nijsseni' complex, and this little group also includes A. panduro, A. baenschi, A. norberti and a few others. They are what I would regard as a 'blackwater' secies, so will benefit from high levels of tannins in the water (will also help soften and lower the pH of the water). Feeding wise, standard frozen food and live food selection will work well (I've never found my Apisto's to get on too well with dried foods).
I would suggest a single pair as a starting point and standard apisto tank setup (sand substrate, bogwood caves, plants etc), easy to sex when adults, female will have a black edge to the trailing ventral fins (both males and females have the red edge around the caudal fin) and the male should be a nice azure blue (female yellow) and exhibit very little (if any) black markings on the body.
The price quoted seems reasonable for adult fish, for the Apisto viejta though, I would say that it was too expensive for that type of fish.
Andrew