PCPartPicker Part List: https://au.pcpartpicker.com/list/zGTTL2
CPU: AMD Ryzen 3 3200G 3.6 GHz Quad-Core Processor ($165.00 @ Umart)
CPU Cooler: Cooler Master MasterAir G100M RGB 22.63 CFM CPU Cooler ($69.00 @ Austin Computers)
Motherboard: Asus Prime A320I-K Mini ITX AM4 Motherboard ($130.00)
Memory: G.Skill Ripjaws 4 series 8 GB (2 x 4 GB) DDR4-2400 CL15 Memory ($58.00 @ Umart)
Storage: Kingston A400 240 GB 2.5" Solid State Drive ($49.00 @ Umart)
Storage: Seagate BarraCuda 1 TB 3.5" 7200RPM Internal Hard Drive ($69.00 @ Umart)
Case: Cooler Master MasterCase H100 Mini ITX Desktop Case $39.00 Centrecom
Power Supply: Cooler Master MWE Bronze V2 550 W 80+ Bronze Certified ATX Power Supply ($89.00 @ Austin Computers)
Wired Network Adapter: TP-Link TG-3468 PCIe x1 1000 Mbit/s Network Adapter ($18.00 @ Austin Computers)
Total: $647.00
Generated by PCPartPicker 2020-07-20 09:07 AEST+1000
Upgrade path for GPU later. Fortnite and School work.
If you can stretch your budget further and get the Couger QBX for $79 instead, you'll be much better off. That H100 has pretty bad thermals.