Is Pepcid Complete ok to take instead of Protonic (it's too expensive)?

Protonix is in a group of drugs called proton pump inhibitors. It decreases the amount of acid produced in the stomach.
Protonix is used to treat erosive esophagitis (damage to the esophagus from stomach acid), and other conditions involving excess stomach acid such as Zollinger-Ellison syndrome.

Pepcid Complete (famotidine, calcium, and magnesium)
Famotidine is in a group of drugs called histamine-2 blockers. Famotidine works by decreasing the amount of acid the stomach produces.
Calcium and magnesium are naturally occurring minerals that neutralize acid in the stomach.
The combination of famotidine, calcium, and magnesium is used to relieve heartburn associated with acid indigestion and sour stomach.

Whilst both drugs work to reduce the amount of acid produced in the stomach you will need to discuss the change of medication with your Health Provider. There maybe a good reason your Doctor has chosen Protonix over Pepcid Complete.