As far as the trachy I'm not sure about mixing with bichirs. King-El has both in his tank but his tank goes against all the regular rules for stocking fish. Available infrequently, not something your likely to find in a store but you should be able to get from a vendor on here. As far as price it seems to really vary by size. A 12" wildcaught one was selling in a store locally for around $150 and smaller specimens going for $40.