Toner cartridges for laser printers never come cheap. However they do last for a long time (compared with inkjet ink cartridges). Dell ship their printers with 'starter' cartridges, which are only half full. Any cartridge you buy should last about twice as long as the starter cartridge. (That certainly applies to the 1100, which definitely comes with only a half-full cartridge. I'm assuming that the same is true of the 1320c).
There are loads of firms which supply 'remanufactured' toner cartridges. e.g. this one:
http://www.focustech.co.uk/contentitempage.asp x?contentid=974440
However, I'm unable to recommend a particular supplier. Unless somebody else can, you'll have to Google 'dell remanufactured 1320c' and 'dell remanufactured 1100' and search through the offers.
Chris