Start by motherboard.
Much better if bundle like CPU + Motherboard + And Ram kahit single channel it's fine kasi canvassing ka lang naman eh.
Athlon 200ge bundle starts @ 4.5 - 5k depende na lang din sa seller kung independent ba ( walang pwesto ) or in store.
Flash Drive you can find cheap naman for 200php 16gb flash drive kahit usb 2.0 it's fine basta used, not fake but brandnew sa shopee, because no guaranteed sa data corruption ng windows installation disk.
And always remember, wag ka bibili na cheap na power supply. Go for a decent ones, kahit may kamahalan at least new and ikaw ng unang user, rather than buying a second hand.