A simple bridge rectifier, storage capacitor and linear regulator would work OK.
If you want higher efficiency a buck convertor is better, but a 'lashup' on a breadboard will almost certainly not work - the devices involve very fast high current switching and need a carefully designed PCB.
You can buy such premade devices capable of up to an amp or so at 5v very cheaply (~£1 ) on eg eBay, and I suggest you go that way.
You'd still need a rectifier and storage capacitor, of course
Allan