The other thing I've begun to consider for credits is those levels where a slot first becomes available, level 19 relics sell for more than higher level ones for example.
I've done this with my Biochem. I can't make enough lvl 21 implants.....mainly because it takes 6 Genetic Anomalies. Needless to say, I've ALWAYS got at least one companion running lvl 2 Bionalysis compound missions. If I'm really running low, I'll go farm Mandalorian Raiders real quick. I probably should go to Coruscant and farm any Heroics (and the rest of the planet as well) for strong beasts to harvest more mats.