Hi,
Check did new PO price of net price 4384.12 USD picking from last PO price from that Vendor history instead of PR price 560 USD.
As you are creating a PO with no material number details only entering shot text where account assignment category used- Better go for development for picking PR valuation price to PO with related Cost object with G/L account. Also do setting in OMET and SU01 for picking/adopt PR price in PO.
Regards,
Biju K