ya you could do an upside down catfish just make sure that there are plenty of places for the cat fish to hide under. And if you dont like the tetras you can always give them to PETCO because they will take them from you.
About a year ago I would see our upside-down about 4 times A YEAR. No lie! I would periodically think he died. He's only single, but I see him now every night @ dinner, as he's decided he likes the pellets I feed the clown loaches.
Tetras are bound to be cheaper. What type are they? Tetras are "stupid" until they're in a real nice school. I'd say add 3-4 of the same species tetra and maybe 1 or 2 of the same Cory species instead of 3-4 upside downs.