Dear Sunita,
Please share your birth details so that I can suggest you the best gem based on your problems.
Regarding your question, Blue Sapphire can be worn in Gold ring or pendant which can give good results. However, one can also wear Blue Sapphire with Silver when advised by astrologer after looking up ones horoscope as silver signifies Moon & Venus and Blue Sapphire signifies Saturn. The interesting part is that; Saturn (Blue Sapphire) is enemy of Moon (Silver) but friend of Venus (Silver); so it may not give the maximum result.
If you are financially capable for opting a gold ring or pendant with Blue Sapphire, then please go ahead. If your present financial situations are not allowing you, then you can go with silver metal for time being or other metals like iron and steel. Please wear it again in auspicious time after cleaning the gemstone with warm luke water.
For your second question, price varies with quality of gemstone. Cut, clarity, color significantly effects the price of any gemstone. It is best to buy from trusted person.
God Bless!!!
Srinivasa Temkar