I used a 04 cbr 600 rr for track last year. It was in road fairings just taped up the headlight and stripped a few bits of it,bought it for 2300 did around 12 trackdays on it and a couple of rideouts then sold it for 2100 in October.great bikes for the track reliable and can pick them up cheap.year before that a triumph 675 and when I get back this year think it’s going to be an 08 plate r6
Check out motoforum.net a lot of racers/track day junkies sell there bikes on there, have a whole section dedicated to selling race bikes with v5’s always loads going although best time to buy is end of season not the start