The OEM rubber mats are ok, and looks like they retail around $50USD... your footwell will still get a little salty but they contain most of it. In my 07 the driver's mat cracked after a few years though, and then it was useless. Kijiji is often a waste of time, but I got a set of WeatherTechs for $30 or $40 on there a few years ago so it may be worth a shot.
This doesn't help you (sorry) because they don't fit an 05 Impreza, but in case anyone else is reading, Findway mats are pretty sweet. $100 for custom fit all weather floor liners, and I like the look and feel of them better than the rubbery WeatherTech/Husky/Rubbermaid alternatives.