Halfrauds sell FZS600 oil filters for about £6. ("Champion" branded)
I buy my oil in Asda (who do a very nice 'own-brand' semi-synthetic 10/40 that ticks all the boxes).
2 oil changes worth for £15 (ish).
Hi-Flo are (were) a marketing outfit from Thailand who make filters.
They used to claim "TUV spec number xxxxx approved" - when you looked up the spec it covered the machining of the screwthread
.
Buy a cheap one ... I've never seen a properly oiled engine with a working oil pump fail for lack of lubrication.