First post, please be gentle :)
Not sure about the lowest, but seems a good price for a B450 mobo ($99+ elsewhere). Ryzen 5 3600 is also on sale for $299 - https://www.shoppingexpress.com.au/buy/amd-ryzen-5-3600-3.60….
The Gigabyte B450M DS3H AMD AM4 mATX Gaming Motherboard supports AMD 2nd Generation Ryzen with Vega Graphics/1st Generation Ryzen processors, Dual Channel Non-ECC unbuffered DDR4, 4 DIMMs and HDMI, DVI-D ports for multiple display. It also has High Quality Audio Capacitators and Audio Noise guard with LED Trace path lightning.
Chipset:
B450
Form Factor:
microATX (mATX)
M.2 Sockets:
1
RAM Type Support:
DDR4
RAM Slots (DIMM/Desktop Memory):
4
Max RAM Capacity (GB):
64GB
RGB Header/Connector:
1
Socket:
AM4
Just keep in mind that you might need a Ryzen 1st / 2nd gen if you want to flash this to work with newer chips?