OK, Let us switch to kanji because English is getting confused. 墨's price depends on its age and the chemicals involved. Naturally dried 墨 is really expensive and it grinds finely, therefore its application will have different effect. If the 硯 is of a low quality, good ink will not reveal its full potential.
Price of 墨 also depends on its size, obviously. But it is a secondary factor to its age (the older the lesser its weight). Old 墨 (like 20-30 years) can be stunningly expensive, especially in Japan. 2000$ for a tiny one (10x1x3 cm) would not surprise me.
硯 - here price depends on thickness of the stone, but most importantly on a quality and size of the grinding area. The bigger the more expensive. Small 硯 is uncomfortable for ink grinding, and it takes more time to prepare it. Low quality grinding area will shred ink into larger particles and it will be visible in work.
With brushes, as I already said, the price depends on the hairs. Wool can be deadly expensive, and mouse or rat whiskers can be ridiculously expensive.
Everything is cheaper in China, though it is much more tricky to buy it without being cheated. There is a crapload of fakes there.
If you buy for business, you will do it in bulk, thus prices will be much lower. Also you will not want to buy from stores but reach the factories directly. I trust you know Japanese.
All four treasures of calligrapher are linked together. If the 墨 is good but paper is of a low quality (too thick and not absorbent, or not dry enough) the line will be dull and boring. Then if both are good but the brush is the weak link, again the line won't be so interesting. This does not mean that for creating a spectacular work you need to spend 50 000 dollars on supplies.
墨 you have provided a link to is not very good. The reason lays in its shape. Simply, it is a bitch to grind. My suggestion is to buy one in a rectangular form, say in a shape of a Snickers chocolate bar, as such:
http://store.shopping.yahoo.co.jp/to...i/kb-0022.html
I also agree with Columbine that decorated 墨 is more for gifts than for practical use. For a large size 墨 you should not spend more that 80 - 150$ (large is 18-20 cm long, 5cm wide and 2-3 thick, such ink will last).
Brushes are a bit more complicated because there are so many of them.
Columbine can tell you what is needed for sumi-e. For calligraphy you will want brushes soft made of wool, harder made of weasel (or other hard hairs), and mixed ones. They all have different purpose. I would not go for the hairs length more than 5 cm. 3-4cm and hard hairs is perfect for beginners.
I doubt many professionals will buy a brush from an online store. I go by train and bus for an hour to my store only to buy paper or brush. I need to touch it, see how thick it is (paper), how dry, also you can try to write on a sample piece. With a brush, you need to check if the hairs are centered, brush is well balanced, shaft not crooked, and hairs responsive and well arranged (forming a sharp ending). Same with 硯, i would never buy one online. I need to touch the grinding surface.
墨 can be bought online, as opposing to 硯 and a brush it does not last long. If you don't like it you simply buy a new one.
The Chinese set you linked to is for kids or those who wanna play with ink a bit to relax. No professional calligrapher will ever buy such thing.
Summarizing, 墨 80-150 bucks for a larger one and 15-30 for a small one.
Brushes, I would say 50-100 bucks for a decent brush.
硯 this will hurt you, as i am not sure you can buy a decent one of a reasonable size for less than 200-300 bucks.
Paper - well depends on a size an purpose. 半紙 i use for practice is Chinese and i pay 25$ per 1000 sheets. Then again, if you want a good one for preparing 作品 you can go as high as 350$ per 1000 sheets.
With size and age price goes up. Recently I bought 18 years old paper for sumi-e, 50x250cm and paid 120$ for 50 sheets.