If you use a printer which uses cartridges which are common to a large number of models from the same manufacturer, you can usually get hold of cheap 'compatible' cartridges easily. (e.g. my Canon printer uses cartridges that cost �2 or �3 each). This is because there are plenty of used cartridges available for 're-manufacturing' or, alternatively, because it's worth an independent firm actually manufacturing their own compatible cartridges (rather than just re-filling empty 'genuine' cartridges).
If your printer uses relatively uncommon cartridges, there won't be many used cartridges available for 'remanufacturing' and it won't make economic sense for an independent firm to make the cartridges themselves.
The cartridges for the F380 fall into the latter category, so you'll always have to pay relatively high prices, even for remanufactured cartridges. However, these are now coming onto the market:
http://www.tonik.co.uk/XC9351A/701543/kzmp/
Chris