Braque was an artist who loved to try out new ideas within his work, and this was partly how the cubist movement came about. He also tried different tools and in the case of this painting, sand was used to add texture to the surface of the painting. If you look at the image below, you will see the close up of certain parts, where sand can be found. He also incorporated pebbles into other paintings, though not here. Besides that, there are clear pencil marks, suggesting that the artist drew much of the composition initially, before then adding oils. This was the normal process that he used for still life, so is unsurprising. The difference here is that the original lines are still so clear and left generally unaltered, where normally oils would then be placed over the top, or close by.
The artist shades various corners of his compositions in order to add the suggestion of shadow, as if the different items of the scene are actually overlapping each other. This piece is one of the simpler artworks from this period of his career, where few colours are used and much is left merely with outline. In other cases he would fill forms with an abundance of oil and provide a much busier look to the final piece. See Violin and Candlestick and Clarinet and Bottle of Rum on a Mantelpiece for examples of that.
Le Violon was purchased at Sotheby's in 2015 for an extraordinary price of 8,202,000 USD, although this was actually some way below the initial estimate which placed a valuation expectation in the region of $12-18m. The media often draw attention to these astronomical prices rather than concentrating on the more wholesome elements of the art world, but they understandably make for exciting headlines and also will be of interest to non-art fans who are interested in investment or general news. The valuations have many different variables involved, with the artist clearly being the most important thing. There are then other elements such as the fame of the particular piece itself, its condition, and also the availability of their careers more generally, which will impact supply. Most of Braque's major work is owned by galleries and museums in Europe who have no intention of selling them, making the remaining pieces much more valuable.