Geez, I didn't expect them to be so pricey :/
Yes, high quality filters aren't cheap. However, there are some gems to be found.
I have a Tiffen circular polarizer, which cost me less than $20, and it's completely fine. Your lens's filter thread is bigger than mine, so it will be more expensive, but that Tiffen is still rather inexpensive.
I don't use graduated neutral density filters at all. While they certainly can be useful, I guess I'm just too lazy to use them. Digital photography opens up a lot of possibilities without the use of filters, and proper HDR technique is a great example of that. I use the 32-bit mode in Photoshop's HDR Pro function. It combines the bracketed shots to a 32-bit TIFF file, which can be manipulated very similarly to a RAW file - after the shots are combined, I save and move back over to Lightroom, and develop it exactly like I do a single RAW file.
I have two standard neutral density filters (standard as in solid, not graduated). One is a Hoya 2-stop filter that I bought very shortly after I learned about the exposure triangle (in other words, when I was an idiot), and a Tiffen 10-stop filter that I bought less than a week after its release. The Hoya isn't a bad filter, but early afternoon sun laughs at the mere 2 stops it blocks, and the Tiffen… well, it's not really neutral. Every shot with the Tiffen is pink. Literally. It has such a terrible color cast that I can't even fix it in Lightroom.
A sensible combination would be two filters, one for 6 stops and the other for 10 stops. LEE Filters makes the best in the industry, the Little Stopper and Big Stopper, respectively, but each costs $140, and requires two additional accessories - an adapter ring that screws onto the filter thread of the lens (the ring for a wide angle lens with a 77mm filter thread costs $60)
and a filter holder that sits on the adapter ring.
I've heard wonderful things about the Camdiox CPRO SMC Nano ND1000 (10-stop neutral density) Filter, which costs $72 in the 77mm-diameter version. They also have a variable ND filter that goes from 2 stops all the way to 10 (its official name: Camdiox CPRO SMC Nano Fader ND4-1000 Filter), and that costs $115 - haven't read any reviews about that one (yet). The argument of regular vs. variable ND filter is sort of similar to prime vs. zoom lens...
But before all that - get a good tripod if you don't already have one.
