What is ok to do with lower back pain at the gym, bike, treadmill, and/or elliptical?

All of them?: The exercises you mentioned when done correctly can all give you your desired result. I usually suggest alternating your cardio machines, thereby decreasing repetitive injury - for example do 15 min on each. Also pls make sure you are doing the correct exercises on each, if anything hurts stop and avoid running on the treadmill - u can always increase incline instead. Hope this helps.