simon - get a USE exposure Maxx D and a triple cell back up for it that should let you run 940 lumens for 6 hours - for your budget you could get a pair of triple cells and run them for 9 hours on full - i rarely run the maxx D on 940 lumens though as its overkill
I run a Maxx D and a Joystick on my head (with a triple cell backup on the joystick)
I just finished 24 hours strathpuffer solo on that set up running the maxx D on medium and the joystick on full bore for the full 17 or 18 hours of darkness - and the maxx D still ran to the end of the race because i didnt turn it off through fatigue.
Cannot reccomend the maxx D highly enough - im sure they also contributed to the melting of snow on the course 
Rory Hitchens and his guys are a really sound bunch of fellas too should you have any issues - the only issue i had was paying him ! (yes ive just given you that sales pitch and now im telling you i payed for them with my own cash ! )
- we now have built up something like 6 set ups like above in the ABC over the last year or 2 with no one having any issues that im aware of - unlike another very premium brand where we got a few sets to test for an(as in singlular) event and every set broke mid lap.
Word up to the trout light though. I would seriously consider them now given i was riding with a chap last night who had the 5 leds in a square block type one (what do you call that trout ? ) and the workmanship and light out put was pretty epic. Tne only downside i could see to that light was it looked like a bit of a pain to swap between helmets/bikes mid race
conversely
Bastid light - one of our group last night had one - it completely self destructed before he got it on the bike - mount snapped - then snapped off the light. He rode with his diablo and the club lights after that - not impressed you get what you pay for and i for one wouldnt be turning up to a 24hour race with that piece of shit - would rather go for some lo0ckblocks and a pair of fenix
