"a blanket cost shared out amongst the "biggies""
Not any more.
Anybody who writes songs or performs traditional material (which is by definition in their own arrangement) can and should join the PRS and if you perform at enough venues where PRS returns are filled in or if you qualify for the "small gigs scheme" (which basically means if you do any gigs at all) you can fill in returns and get payments.

It costs a one-off payment of £100 to join, and we got most of our money back on the strength of one Sidmouth Festival.
And we're not pop stars...

Anahata