Be sure to check out KEH and eBay as well.
I've got 52mm Hoya and Tiffen Yellow, Green, and Orange for sale in the forums
(need bigger filters for my ETRS, they're probably too small for a 645)
But yeah, to reflect what TUco said, filters help a lot. It takes some practice to figure out what colors will do well in which situations, but it's helpful to spot meter through them at different tones in the scene. Contrary to what I thought/read before, I now use a green filter in the SW with film to help darken the nice red sandstone. I'll usually have to burn the sky in while printing to keep it from going totally white, but it helps the tonality in the rocks/ground out here. Red makes for a nice dramatic effect, but it's easy to overdo, and out here it can make the nice tones in the rock a uniform grey...
A good kit to start with would be Yellow, Red, Green, with orange less of a priority. If you can find a scene with lots of varied colors, try bracketing with all your filters to get the feel for what they can do.
Also, keep in mind, filter factors are only a guide. Once you get the hang of what the filters can do, you can estimate the effects and expose for your shadows with detail (zone III). Also, a 25A (red) filter has tricked most of my in-camera meters... It's a bit dark to focus through with slower lenses, so I'll usually meter off a nice darker/shadowy green and then add 2.5 stops (FF of my red filter)