For 54 caliber Great Plains flintlock:

1 lb GOEX FFFg @ $10.16 per lb. with 80 grain charge = $0.17 per shot.
Hornady .530 balls @ $11.91 per 100 = $0.12 per shot.
1 yard Walmart pillow ticking @ $3.49 per yard yields1152 patches = $0.003 per shot.
1 black English flint @ $1.50 each yields 40 shots (average)= $0.04 per shot.

TOTAL: $0.33 per shot (cast your own balls with free lead= $0.21 per shot).