Muriatic acid is not recommended for passivating stainless steel because it can leave behind chlorides that can cause corrosion.
ASTM A380 is a standard for passivation of stainless steel that provides guidelines for the passivation process and the testing of passivated surfaces.
The cheapest stainless steel finish is typically a brushed or satin finish, which requires less processing and polishing than a mirror or high-polish finish.
The cheapest grade of stainless steel is typically 409, which is commonly used in automotive exhaust systems.
It is recommended to passivate 316 stainless steel to restore its corrosion resistance and ensure its long-term durability.