Right now I am testing Alkalinity, Nitrate, and Phosphate daily, and Calcium every other day. The consumption is the same as it would be if testing manually (prices from BRS):
Red Sea Alkalinity Refill: $18/75 tests = $0.24/test
Red Sea Phosphate Refill: $23/100 tests = $0.23/test
Tropic Marin Nitrate: $27.60/50 tests = $0.55/test*
API Calcium: $10.25/29 tests =$0.35/test
At my aggressive testing schedule, this means a cost of $1.19/day.
*Note: A refill kit for Tropic Marin Nitrate apparently exists, but is not sold online anywhere in the US. It is available in the EU, but with prohibitive shipping costs. Purchasing refills for 350 tests (a years supply for me) brings the cost per test down to around $110/350 tests = $0.31/test.