The cheapest full ATX AB350 based board I can find anywhere, normally retails for around $125 dollars, marked down to $99 on PCCG but UMART has beat them with $85.
Fatal1ty AB350 Gaming K4
ASRock Super Alloy
Supports AMD Socket AM4 A-Series APUs (Bristol Ridge) and Ryzen Series CPUs (Summit Ridge)
Supports DDR4 2667
2 PCIe 3.0 x16, 4 PCIe 2.0 x1
Graphics Output:HDMI, DVI-D, D-Sub
7.1 CH HD Audio (Realtek ALC892 Audio Codec), Supports Creative SoundBlaster Cinema3
6 SATA3, 1 Ultra M.2 (PCIe Gen3 x4), 1 M.2 (SATA3)
8 USB 3.0 (1 Type-C, 2 Front, 5 Rear)
Realtek Gigabit LAN
Not sure what makes this board "Gaming" grade other than the Fatal1ty brand name. But it's cheap, there are two M.2 slots that you can put SSD's into and you should consider one if you're building a Ryzen PC without sacrificing any must-have features (overclocking support, USB Type-C port, and loads of rear I/O ports with USB 3.0 etc).