Some generally common/inexpensive options
Archerfish (Genus Toxotes)
While many are brackish and/or too large, certain species like blythii and microlepis would be good fits.
Ropefish AKA Reedfish (Erpetoichthys calabaricus)
Interesting and fairly hardy oddball. Close to bichirs, and far more active than some would think.
Spiny Eels (Family Mastacembelidae)
There are dozens of species. Many would be appropriate.
Freshwater Needlefish (Genera including Xenentodon, Potamorrhaphis, Belonion, more)
Interesting, gar-like fish. Most common is X. cancila.
There are tons of fish that fit the bill. Those are just some suggestions.