Your search for "QSFP-40G-ER4" revealed the following:
Arista QSFP-40G-ER4 BASE-ER4 40GB SMF QSFP+ Transceiver
SKU: NSH-7544
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 2,029.99
• Only 2 remaining
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NEW Cisco QSFP-40G-ER4 40GB BASE-ER4 1310nm SMF w/ OTU3 QSFP Transceiver
SKU: NSN-2309
Condition: New
Shipping: Overnight Options
Warranty: 365 days
Dell QSFP-40G-ER4 40GB BASE-ER4 Extended-Reach 40km SMF LC QSFP+ Transceiver
SKU: NSB-5955
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
Cisco QSFP-40G-ER4 40GB BASE-ER4 1310nm SMF w/ OTU3 QSFP Transceiver
SKU: NSH-5563
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
Juniper QSFPP-40GBASE-ER4 40GB BASE-ER4 1310nm SMF 40km QSFP+ Transceiver
SKU: NSB-3530
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
NEW Juniper JNP-QSFP-40GE-ER4 40GB BASE-ER4 1310nm SMF QSFP+ Transceiver
SKU: NSN-6363
Condition: New
Shipping: Overnight Options
Warranty: 365 days