I am going to shoot long expo rivers and waterfalls, I have no ND filter yet. I am researching now and I was adviced to use ND-64 for the best result. As I see on amazon there are some different brands with different prices, I am not ready to pay much money right now and want to access ND filter (67mm) that will not be cost expensive and does the normal quality job. So, can you advice which brand to buy?
When it comes to filters you can get cheap filters. You can get good filters. But you can't get cheap good filters.
There are filters available for 67mm threads that claim to be 6 stop (ND64) filters available for $30 or less. They tend to be of poor optical quality, don't really have the density they claim (most of the cheapest ones are more like 4 stops, if even that), and impart a color cast to the images taken with them.
At 67mm and ND64/ND 1.8/6-stop reduction the price for quality is a little higher.
You can get a B&W 67mm ND64 single coated filter for about $67. That will work OK as long as you aren't shooting in situations where ghosting might be a concern. The next step up is something like the B&W 67mm ND64 multi-coated filter for about $118. Both sides of the filter glass have eight coats on them that eliminate the reflections that cause ghosting and other types of lens flare.
If you are shooting with a very wide angle lens the thicker rings of the two filters above may cause vignetting (making the edges of the image darker). In that case you might need a filter with a "thin" or "low profile" ring such as the Breakthrough Photography 67mm X3 6-Stop MRC16 for around $160. The X3 series of filters are made from high quality glass, have low profile mounting rings, and are weather sealed in addition to using 16 layers of multi-coating.
Breakthrough Photography is a relative newcomer in the filter arena but they have gotten a lot of very good reviews and the optical quality of their filters compare favorably to other, more established brands that cost quite a bit more.
The other question you need to ask yourself is whether you want to use screw-on filters at all, or whether you want to use a square system, such as the Cokin or Lee systems, that use square/rectangular filters and a single holder attached to the lens with various ring adapters for the different lens thread sizes in your bag.
The advantages of the square systems is that you can use high quality filters without having to buy a new set every time you get a lens with a different filter thread size. They are also more flexible to use from a compositional standpoint with graduated neutral density filters. The advantages of the screw-on types are that they are usually cheaper per filter.