if you need something on a budget that is an actual upgrade from your 5820k get the 2700 (x if you can find it for $10-20 more) as it is faster and it has been going on sale for months months now. You can pair it with something like the MSI x470 Gaming Plus, it is only sale often for $110+ and it can also run the 3900x/3950x at stock speeds.
Ryzen 2700
MSI x470 Gaming Plus
DDR4 3000Mhz CAS 15 or 16 2x16Gb (Cosair Vengeance LPX CMK32GX4M2B3000C15 if you can find it)
Use all your old parts, expect using the stock cooler with the Ryzen.