Why does the price of a single SFP-10G-SR transceiver range from $31 to $700? same brand, same module, but different site, very different price

We got a quote to to buy 10pcs of cisco 10G SFP+ transceivers @ $500 each. that's $5,000 total.

I see the same cisco sfp-10g-sr on amazon, newegg at $31, $40, some sites have then for $150.

they are all cisco brands too and i cannot find any difference.

can someone help me out in explaining why the price difference?

how much should they cost?

thanks