I've hired track bikes before when on Focused Events days. They were in good condition and I though reasonable cost given wear and tear and fuel.
I found it takes a couple of sessions to get to know the bike (brakes, tyres, riding position) and you never know how many heat cycles the tyres have been through and tyre warmers are usually an extra.
The excess is very high given you may just break a clutch lever and get charged the full whack (£500 or £600 is normal) and it will be the end of your day. If you have a big off of course it would save money but I found I didn't enjoy the day as much.
That said, you can thrash the nuts off it and it is nice turning up in your car though with no loading/unloading/van hire/trailering worries
