I'd recommend standard 'torch' looking lights rather than large 'spotlight' lights. With the increasing technology, there is not a massive difference in light output or performance, and when running on rechargeable 18650 batteries they'll last all night (and extra batteries are cheap, so carry spares anyway). They're much lighter lights (haha - I mean they're less heavy) and much more compact.
Also, it's quite possible to be running some really cheap lights and mounts, and still get excellent performance.
A 1200 lumen spotlight torch, 4 rechargeable 18650 batteries (two to use, two spare), battery charger, and mounts could all be had for around $70 - $80 posted. Throw in another medium-output torch or two for hand-held use and another two batteries, and $100 will have you completely set up. Check out Deal Extreme (www.dx.com).
I'm using a setup from Deal Extreme and I'm very happy with the performance for the price I paid.
Having said that, I'm not running it on a large calibre cannon - it's on my .223 rabbit/fox gun, and occasionally underneath the 12 gauge. I'm quite confident that it'll be able to handle some medium calibres anyway, so as long as you're not using a .458 Lott to spotlight bunnies, you should be fine.