Polarized filters can eliminate glare when shooting in harsh lighting conditions. Works well for things such as darkening skies and eliminating reflections from leaves and water. You would need to be facing 90 degrees from the sun to achieve the effect however.
Nice, so it sounds like Polarized filter would be the most useful. Do they make lens hoods that will fit on the 30mm?
A 43mm filter would fit perfectly. As far as a lens hood is concerned I'm sure there are some cheap ones on ebay that you could purchase.
As far as prices are concerned I've never had any issues with polarizers. I have an off brand 67mm polarizer for the 85 1.4 and a tiffen 72mm polarizer for the 16-50 S.
I do have an ND filter that was my most expensive purchase. It's a Hoya 72mm ND 400. ND filters are probably the only filter that you may not want to cheap out on but I can't see myself spending upwards of $100 for them.
Best of luck with your purchase