The heaiver-than-lead shells are not cheap. Generally speaking, ammunition is one of the cheaper parts of a turkey hunt.

More important than pellet composition or shell length...Pattern your gun, and go with what the holes in the target tell you.

However, to save a few $$, get 3" shells and go with a tried and tested load of copper plated lead shot; Win. Supremes or Federal.

For non-toxic, heavier-than-lead, I like 3" hevi-shot #4 and 3" Rem. Wingmaster HD #6. Make that my gun & choke tube combination likes...

For a good lead load, I'd recommend 3" Win. Supremes in #4. Note, all this is based on an assumption that you're shooting a 12ga. 20ga loads may be cheaper, while making the gobblers just as dead.