How to manage sales cost due to fluctuating raw material costs

Hello,

I have a few questions relating to raw material costs affecting sales order quotes. The issue that we have is that the raw materials that I buy are constantly changing, which slowly increases/decreases (mostly increases) the COGs. 

Does the COGs pull from the last purchase order? If so, how quickly does the price change? Is it once the purchase order has been invoiced?

If I have a supplier that tells me they can offer me a raw material at a certain price, but I don't need to buy yet, should I enter the offered price into price list entry or RFQ? And does the supplier with the lowest price transfer to a purchase order?

I'm constantly getting price quotes and price changes, and I don't know the best way to manage all of this through Sage. Additionally, I buy thousands of raw materials that fluctuate based upon the market so it's hard to remember when I get a better price unless i go to each supplier every time I order something. 

Any insight will greatly appreciated.

Thank you

Danelle