For exactly the same part number?
If not, there might be subtle technical reasons that impact cost.
But even if the same part number, from different sellers, or as far as you can tell, technical specs are identical for different part numbers, they might still differ much in price.
Well, there's always the "you get what you pay for" but truthfully sellers will price products to try to be as profitable as possible. Lots of factors go into product profitability, beyond the obvious of just setting a high sales price. (The factors can be so complicated and intertwined, why colleges/universities even have business curriculums to teach such.)
I will also note, in general (cannot directly address Cisco pricing due to NDAs), when dealing with merchants, unit price is often also impacted by quantity of items being purchased and/or overall total order value. (Go to any car dealer and mention you want to do a fleet purchase, likely you'll find unit prices discounted.)
There's also factors like, even though those transceivers might be legally sold, will Cisco warrant them if purchased from an unauthorized seller? Possibly not, but if there is an 8.5x price delta (according to the prices you provided), even if you need only one, you might buy two or three and take your changes.
