I bought one on Amazon for $115, however it's priced a little higher now. It's possible that the price fluctuates. It's OEM and is shipped from a Mazda dealership.

https://www.amazon.com/dp/B082WNXV32?ref=ppx_pop_mob_ap_share

it’s $150 now! But if you want the link, here you go. Mazda New OEM 2020 CX-30 Rear Trunk Cargo Tonneau Cover Board DGH9-68-310-02 https://www.amazon.com/dp/B082WNXV32/ref=cm_sw_r_cp_api_glt_fabc_VXTR7R8J96J6MF54QYQM?_encoding=UTF8&psc=1