Hi,
DDR3/4 prices are tied to MEMORY prices in general which includes different types of flash memory. SSD's, camera cards, VRAM and so on.
There are plenty of ESTIMATES but so far it's really vague and could be in two months, or even a YEAR from now before prices drop noticeably.
On top of that we have the Graphics Card prices due to crypto-miners. That may be a non-issue in four months but who knows.
(I'd also consider COFFEE LAKE from Intel instead of AMD Ryzen depending on performance results and the prices. The 6C/6T (6-core no hyperthreading) i5-8600K looks really interesting if it costs about $260USD!!
It may be up to 50% faster per core than the R5-1600 (after both max overclock) so even with SMT/Hyperthreading with full...