Thanks very much for the help guys, I really appreciate it. If I'm correct I could use the following element:
Strip Heaters
Using 5 of the 'HCS-237' elements I would have a total power rating of 5kW. As far as I'm aware, as long as these elements dissipate the required amount of power (and I can use a potentiometer in series to control the load more precisely), I can go for the cheapest combination. I'm not sure if these heaters require fans or not, though.
What do you think?