TigerDirect.com has 4GB (1x4GB) Crucial Ballistix Sport DDR4 Desktop Memory (BLS4G4D240FSA) for $49.99 - $20 Rebate = $29.99. Shipping starts at ~$4 and may vary depending on location
TigerDirect.com also has 8GB (1x8GB) Crucial Ballistix Sport DDR4 Desktop Memory (BLS8G4D240FSA) for $99.99 - $30 Rebate = $69.99. Shipping starts at ~$4 as well.
Notice: If you need to buy four modules for an X99 platform you'll need two people to buy the modules as there is a limit of 2 rebates per person.
Limit Two (2) rebate per qualifying rebate offer, per person, billing address, company, household and receipt/invoice/packing slip during the eligibility period, except were prohibited by law. Only one (1) rebate application per envelope