Steely CBR600. Mine's not for sale because it's too much fun. We've done 10 trackdays this year together and it's been lent out to two trackday instructors for another 5 days on track. They will hold their own in the fast group in the right hands.
As for preperation, I made money from prepping mine - I sold all the road gear like lights, mirrors, indicators, l/h switchgear etc on ebay and bought a new set of Rennsports. That left me 30 quid up. I blanked off the headlight hole with a bit of broken gixer fairing I had kicking around. The forks benefit from 15W oil with the same air-gap, that stops them diving on the brakes too much and makes the rebound more controllable. My shock is tired so I lashed out 75 quid on a used Maxton that will require a 200 quid rebuild, but that's still much cheaper than any aftermarket budget shock worth buying and I get the bonus of the rebuild and adjustability of a quality unit. The only other thing I did was fit some crashbungs from a guy on ebay, they were half the cost of R+Gs and I've seen them work just as well on crashed racebikes.
As it stands my CBR owes me about 450 quid but that will increase when the shock goes in. It's still a dirt cheap way of getting on track, because you'd spend twice that much rebuilding after a simple low-side on your Daytona.