Melting route, cleanliness, inspection level and paperwork. The same UNS number can be vacuum induction melted and ESR refined, or air melted, and those are not the same product even though both meet the composition. Ask which melting route the quote is based on before comparing prices.
Composition is the cheapest part of the specification
Hitting a chemistry table is what any melt shop can do. What separates one quote from another is everything around it: how the heat was melted and refined, how clean the steel is, how much testing was done, and what paperwork travels with it.
A vacuum induction melted heat refined through electroslag remelting carries a very different cost from an air-melted induction heat of the same nominal composition. The certificate may look similar. The inclusion content and the segregation will not be.
The four things that move the price
Melting and refining route. VIM, VAR, ESR and air melting are different processes with different yields, and some grades are effectively only made one way.
Raw material charge. Nickel, molybdenum and cobalt trade on their own markets, and a scrap-based charge behaves differently from a virgin one. Two quotes a month apart can differ for no reason except the nickel price.
Size and quantity. A heat has a minimum weight. A 300 kg order and a 3 t order from the same heat do not carry the same price per kilogram, and a small order in a large section may be impossible rather than merely expensive.
Inspection and documentation. Third-party witnessed testing, 3.2 certification, extra NDT or destructive sampling all add cost, and add lead time as well.
How to compare two quotes honestly
Put them side by side on the same specification: standard, delivery condition, mechanical properties, grain size, NDT level, certificate type, tolerance and quantity. When two prices differ by a factor of two, they are almost never the same product — one of those boxes is empty on one of the quotes.
Ask each supplier to state the melting route in writing. It is a reasonable question and the answer is diagnostic.