Prozac is an SSRI and Cymbalta is an SNRI. Prozac won't affect your norepinephrine level and will only affect your serotonin. Effexor is a cheaper SNRI that should gives you less side effect by preventing a norepinephrine withdrawal that might happen during the switch to Prozac.
Please consider that I'm not a doctor and this should be discussed with your doctor.
I was also on Cymbalta and had to switch due to the cost. I went to Citolapram and have excellent results.
I have been on effexor for two years and I can tell you without insurrance it is not cheap.Also it is one of the hardest drugs to withdraw off. I also was on citolapram but my doctor pulled me off it when he saw alot of mood change and weight gain. But then I was on both effexor and citolapram, highest doses each. This could of had some effect. I have been off both 8 months and the withdrawls are alful. I asked my doctor about it and he told me it was the effexor. I hope whatever you do works for you but myself I want little much more to do with any antidepressant do to the effects they have had on me and family members. Good luck