Whats the stuff you're supposed to use to clean your rotor if you get hydraulic fluid on it?

Is it something I can get hold of easily without having to buy a bike (ripoff) version?

Soap and water. Lots of it – or washing powder but rinse very well.

Or any degreaser

Meths is pretty good (not white spirit!), and I think it is (essentially) nail varnish remover in a spray that muc off sell as disc brake cleaner. The proper stuff is better than meths, though, and it doesn't half make you light headed.

I'd say, meths first then proper Muc Off Disc Brake Cleaner if that won't sort it.

Try Isopropyl Alcohol (B&Q, Homebase, etc.), also known as rubbing alcohol.

Cheap, and leaves no residue. Put some on a paper towel, clean disc, wipe off with clean paper towel.

Job done.

EDIT: Don't use this inisde! The vapours can mess with your head, even outside I still had a headache after cleaning both discs.

can of brake and clutch leaner from halfords, about £3

Maplins does IPA as well.

Don't use brake and clutch cleaner!

It can leave a residue that's fine for cars because the heavy duty brakes burn it off, bikes can't do that.

EDIT: Don't use this inisde! The vapours can mess with your head, even outside I still had a headache after cleaning both discs.

Wuss 😉

I've never noticed any effects from it & I use it inside on electrical stuff