Old bikes are not a cheap hobby any more.
They used to be, 40+ years ago.
Back in 1964-ish I needed one of these lamps, and a tank top instrument panel; I went to old Perce Rye in Fulham, bike breaker, open on Sunday mornings till the pub shut.
"Upstairs son, in the corner." So there were, a big pile of them, all 8 inch Lucas, I can't remember what I paid, but the instrument panel, with all instruments, cost me 10 bob, thats 50p to you.
The 1938 500cc bike I wanted them for came free, off a council tip. Still got it.
See what I mean?
Bung any old headlamp on it, and ride it, everybody wants a prize winning bike, not many know how, or have the right bike to start with.