Personally I would look for something secondhand on ebay. Providing you stick with "known" makes you shouldn't have a problem. There isn't a lot which can go wrong with lights and, if it does fail, then they're usually easy and cheap to repair. I would suggest, in order of preference:
1. "Arri" as a search term then look for junior or fresnel lights in the 650 - 1000w range. the 300w are a bit weak for what you want. Next have a look for Arrilite 800w units, not as versatile as the fresnels but built like tanks and will last for years.
2. "Redhead" as a search term. Good makes are Photon-Beard and Ianiro. Watch out for cheap new gear from China or Eastern Europe. Better to buy a decent secondhand reputable make than a unit which will fall apart after a couple of knocks.
When you get a light, have a play with it before you use it in anger. A few hours spent in finding out how the light reacts when you bounce it, diffuse it and gel it is a good investment. If you haven't got a reflector, a sheet of 1m x 1m white polystyrene gives a lovely soft light.
Edit: This is the sort of thing to go for: For secondhand kit, don't spend more than £150 for an Arrilite, £200 on a fresnel or £100 on a redhead. Watch out for those "too good to be true" offers from Korea, Romania, China etc. etc.
http://cgi.ebay.co.uk/Arrilite-800-t...d=p3286.c0.m14 http://cgi.ebay.co.uk/Arrilite-red-h...d=p3286.c0.m14
This seems a nice secondhand kit:
http://cgi.ebay.co.uk/3-x-QuartzColo...d=p3286.c0.m14
It's worth spending a bit extra to get decent lights. I still use kit I bought twenty years ago so it's a good investment.