Let's start from addressing the form of the question posed, as the use of tense is crucial here. It is true that nowadays in some regions brown rice is cheaper than white rice, but the issue referred to, namely the thiamin (vitamin B1) deficiency was largely a problem in 19th and early 20th century, addressed in 1910s by Gerrit Grijns and especially Kazimierz Funk in his seminal research on the milk and rice bran that resulted in the discovery of the vitamins.

Initially the illness was thought to be caused by the intestinal bacteria. This was the theory pursued since 1886 by Cornelius Pekelharing and Cornelius Winkler from Utrecht University. Their assistant, Christiaan Eijkman (Nobel laureate of 1929) noticed that the chicneks he experimented on stopped to display deficiency symptoms after incidental change of the fodder consisting of unprocessed, raw rice. He thus posited that the rice is producing some kind of toxin responsible for neurodegenerative symptoms that is countered by and unidentified factor present in rice bran. Eijkman's colleague, Gerrit Grijns suggested however, that it is also possible that bran is simply containing some substance that is necessary for the proper functioning of the nervous system, to what Eijkman agreed in 1903 as the further experiments seemed to corroborate this theory. This, however, resulted only in the attempts to isolate and synthesize that substance instead of usage of unprocessed rice. Beriberi was also researched by William Braddon, British military doctor examining various tropical diseases who also suspected that the process of polishing rice destroys some important nutritional substance, although he considered it to be an essential amino acid. After sharing his theories in 1910 with Charles Martin, Director of Lister Preventive Medicine Institure in London, the latter asked Kazimierz Funk to continue Braddon's research. Funk quickly discarded the initial theory, stating that the crucial fator is most likely not an amino-acid but a simple nitrogen-based compound. In the next year he managed to isolate the substance preventing the symptoms of beri-beri and name it 'vitamine' due to its health-promoting properties. As a side note, this name cause a bit of stir as soon after other, similar substances were discovered and other doctors suggested that the name 'vitamine' is not correct as its erroneously suggests that all of said substances are amines and proposed various different names. This have been finally resolved in 1920 by Jack Drummond who proposed to shorten the name to 'vitamin' (names ending with '-in' were often used for newly discovered substances) and use subsequent letters of alphabet to differentiate them, leading to the naming convention that is still used today.

The medical neurodegenerative condition caused by the thiamine deficiency, commonly called beriberi (also spelled beri-beri) has been observed in southeastern Asia, especially among people who had little choice over their diet, such as soldiers, sailors, prisoners, hospital patients or residents of homeless shelters. Such people were usually confined to a specific location for a prolonged time, and thus were dependent of the stored provisions that consisted mostly of ubiquitous polished white rice. This choice was primarily caused by the fact that the white, polished rice can be stored for a far longer period than the unprocessed brown rice and thus was preferred whenever stockpiling was necessary. This difference is caused by the presence of natural oils in the bran and germ that is exceptionally high in the case of rice (reaching 25% in bran, as opposed to 4-5% in wheat and 1.5% in barley). These substances, although of significant nutritional value are prone to rather quick decomposition rendering unprocessed brown rice less nutrition and far less appetizing due to rancidification with an additional chance of poisoning as many products of the fatty acids oxidation are severely toxic to humans. Given that rancid fatty acids may facilitate decomposition of vitamins and amino acids as well as the production of insoluble protein polymers decreasing protein adsorption, people observed that those who eat spoiled rice get weak and sick what have led to the common practice of processing rice prior to storage. Rancidification can occur withing several months, making long-term storage of the unprocessed brown rice unpractical. Today it is alleviated by washing, parboiling and packaging the rice in the protective atmosphere, but it still has shorter shelf-life than the polished white rice that can be stored for over 20 years, conditions permitting.

Beriberi was very rare among people with an access to diversified diet, as vitamin B1 is quite common and can be found in meat, fish, grains and lentils that were commonly eaten (Funk noticed that the disease was generally non-existent among people who were eating predominantly white rice but also wheat as opposed to those who ate only rice as their staple cereal).

Last but not least, the notion that the brown rice is more expensive than the white one is purely modern concept caused by the difference is storage mentioned above. The more perishable are the goods, the higher the chance that they may get spoiled and thus, to avoid waste and resulting loss, they are produced in smaller qualities, often much lower that the market saturation margin or the inevitable loss is factored in the final cost, resulting in higher retail price of the less stable products. Historically, the opposite was often true, with the additional processing increasing the cost and shelf life being of little concern, as majority of goods were usually consumed within a short time period.