Here's my recommended list
Ryzen 3 2200G - $125 - Potent little chip. Can be OC'd. Comes with cooler.
Gigabyte B450M mobo - $87 - 4 RAM slots so you can add RAM later without having to throw away the stuff you buy now.
2x4GB DDR4-3000 RAM - $92 - Higher frequency boosts AMD CPU performance.
Crucial MX500 M.2 SSD - $67 - Speedy starter SSD, enough to run a snappy system, get a cheap 1-2TB hdd if you need extra down the road.
MSI RX570 8GB - $200 - Probably overkill, but better price than lower performing cards like the GTX1050Ti.
Cooler Master Lite 3.1 - $45 - Kids like windows and RGB lights.
Corsair CX450M - $45 - Good reliable modular power supply.
LG 24MP59G - $160 - 24" IPS monitor with FreeSync range of 40-75Hz.
My PCPartPicker list total at $873 CAD doesn't seem to be showing mail in rebates (including but not limited the $20 MIR on the GPU and the $20 MIR on the PSU I linked earlier). Which I factor heavily into my purchasing decisions. My total is $825 with MIRs considered.
For Windows license, I'd visit some place like kinguin.net or similar. Toms did an article on this recently (
link here)
Try to get a free keyboard and mouse from either your employer (most companies buy Dell/HP/Lenovo and get a keyboard and mouse with every computer purchase, so they've got boxes of new unused keyboards and mice) or try your local e-waste recycling center.