Starting to compare mechanical components pricing based on a single component (metal prices) can only give you a very, very rough idea, and might be completly different depending on valve size, type, pressure class, type of fabrication etc. etc. Prices will also vary over time and with accessabillity of the material in different part of the world.
A site commenting on this is for instance given by below link.
Extract from the page: 'This page is includes information on the costs of different metals used in mechanical engineering. When producing mechanical components the material costs is generally of limited significance . Other costs should be included when comparing materials including design, procurement, production control, forming, machining, finishing, distribution, etc etc. A component lifetime costs include maintenance, corrosion protection and recovery (scrap).
The raw material cost for a particular component may be 20 times the cost if made from one material compared to another on a weight to weight basis. However the lifetime costs may be very similar if all of the other factors are also taken into consideration.
The material cost of a mass produced investment casting item may be 80% of the final cost. The material cost of a single complicated machined item may be less than 10% of the final cost..
It is not possible to provide cost comparisons between different metals to any level of accuracy. Each metal is varying in price on a day to day basis and different alloys of the same metal can have significantly different costs. A grade 7 titanium alloy costs twice as much as pure titanium (grade 1,2 or 3).
Comparing costs should only be based on final installed costs. eg. for a domestic, industrial piping system a screwed steel system would cost about 40% more than a copper piping system...
Example :
The price of a titanium /titanium alloy products results from a number of factors:
Alloying grade .some grades e.g with Pd alloying component, can significantly increase the price of the alloy.
The purity of the grade... the more pure the higher the cost
The test and inspection requirements;
The procured quantities. The more ordered the lower the specific cost
The geometry ..rolling or forging affects prices per volume or weight
Demand ..e.g High defence demand for aerospace industry can result in higher metal prices
Local economy.. Metal availability '
