How low will RAM prices go? That's a good question, though we are content to watch them keep sliding. If you are need of an upgrade right now, though, it's a good time to pounce. Corsair, which makes some of the best DDR4 RAM, has a 16GB DDR4-3000 Vengeance RGB Pro kit that is available for $84.99.
The caveat is that you'll need to enter coupon code MAYSAVE19 at checkout, via Google Express (Best Buy is the actual seller). It's intended for first time orders, and knocks 20 percent (up to $20) off the tally. In this case, you get the max $20 discount.
Corsair 16GB Vengeance Pro RGB | DDR4-3000 | $84.99 (save $30)
This same kit sold for more than twice as much around this same time last year. It offers a good balance between capacity and speed, and is attractively priced. Use code MAYSAVE19 for full discount (applicable for first time orders). Buy at Google Express (via Best Buy)
Having 16GB of RAM is generally considered the sweet spot. We don't recommended going as low as 4GB these days, and while 8GB will get you by, 16GB is preferred.
Over on Newegg, there are quite a few kits of the same capacity and speed for around the same price. However, this one of the cheapest RGB kits in this class, and it's a low for this particular Corsair SKU. This same kit sold for close to $200 around this same time last year. Have a look at how it's trended (Amazon pricing):
Even as early as last month, this kit was going for around $140. At the price it's at now, after discount, we can confidently recommend pulling the trigger.