If you're on either on a concurrent Intel or an AMD platform, DDR4-2800MHz doesn't mean much in terms of performance since AMD's RYzen loves ram to be at or above DDR4-3200MHz. The same is said for Intel's platform since the 6th generation came to be.
That being said, what are your current specs? List them like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Just because it's listed on Newegg as 100 per stick, doesn't mean you can sell them at the same price, used.