Aluminum and stainless steel are the most multipurpose and commercial materials. Stainless steel is mainly used in kitchen cookware and appliances, processing industries, and infrastructures. Whereas due to lightweight aluminium is used in the aviation industry, cycles, and cars, etc.
Stainless steel has extreme strength and it comes with a price. Stainless steel is a big family of several classes and amalgamations. Stainless steel grades are composed of iron, chromium, nickel, molybdenum, etc. The alloying agents are quite expensive and importantly nickel. The nickel prices are fluctuating and volatile, which indicates the price for stainless steel. The 200 and 400 stainless steel series are less expensive than austenitic stainless steel i.e. 300 series.
Aluminum may look expensive in cases when it is compared with stainless steel in terms of weight. Aluminum is around one-third of the weight of stainless steel. Aluminum is cheaper for the same volume of stainless steel, but it is expensive for the same weight.
Both materials feature pros and cons, but what matters is the appropriate use in applications for a long time. So in comparison aluminium is typically cheaper than stainless steel.