I realize this thread is old, but I thought it was of great interest. I've done freelance Japanese to English translation work. I also did my doctoral studies at a Japanese university and have done some archival work there (though it was with diplomatic documents rather than military ones), so I thought I'd make a few comments from those perspectives.
Looking at the scanned pages provided, the language in Senshi Sosho was much, much better than I was fearing after reading some of the comments here. The main text uses modern spelling and orthography and is pretty easy to read. The biggest difficulty would be when it includes extracts from contemporary official documents, but (again, judging by the pages posted here) that appears to be a minority. I was also pleased to see how little text there was per page. And it's not handwritten, which automatically makes it a lot easier than a lot of sources from that time.
Of course, reading and translating are different things. In addition to the difficulties mentioned in other posts, I'd also note that names would be an absolute monster to deal with. Not only can Japanese names written with the same kanji be pronounced different ways, but the books will be filled with Japanese approximate transliterations of foreign individuals and places. For example, one of the provided pages makes a reference to the main force of the 33rd Division advancing along the "Papun - Birin - Morumen road". If you're not familiar with Burmese geography and pronunciation, it'll probably take some time to work out that "Morumen" is Mawlamyine/Moulmein. Also, since the volumes seem to rely upon Allied documents as well, you'd want to copy quotations from the original sources if possible. Of course, these are really only important factors if you're going for professional quality translations.
Regarding the translation cost, this is something that you'd pay someone a salary for, rather than pay per word/volume/page. That would work out to a much lower rate for the translator, but be more than made up for by the amount of steady work.
This is also something that might make an interesting project in a few years, once volumes start falling out of copyright and the digitized versions and placed on-line.
Here's a quick translation of the page posted earlier, so there's a comparison with the machine translations. I tried to keep rephrasing to a minimum to make it fair.
Overview
Pearl Harbor
(see illustrations no. 1 and 2)
The "Phony War" in Europe, in which both both camps were aligned along the Maginot and Siegfried Lines glaring at each other without attacking in the fall and winter of 1939, ended with the German army's invasion of Denmark and Norway in April 1940. At around the same time, the American Pacific Fleet moved from its base on the western coast of the United States to Hawaii for annual military exercises. Unlike in most years, it did not return home [afterwards], but was ordered to remain in Pearl Harbor. This was May 7.
In response to a question from Pacific Fleet Commander Richardson, Chief of Naval Operations Stark explained that "the fleet will remain in Pearl Harbor until further directed. Its purpose is to deter the Japanese government from taking advantage of the Dutch defeat and the difficult position of the British and French by advancing south." In other words, President Roosevelt's thought that the watchful gaze of this waiting fleet could deter a Japanese advance into the Dutch East Indies after the German army's invasion of the Netherlands, and a rapid move by the Japanese army into Indochina as the French military situation neared desperation.
Pearl Harbor was a large US Navy base that was located in the south of Oahu, the main island of the Hawaiian Islands and was capable of accommodating a large fleet.
Geographically, it was 2,100 nautical miles from San Francisco on the US mainland, 3,300 nautical miles from the Japanese home islands, and more than 2,000 nautical miles from the nearest part of the Marshal Islands.
The Pacific Fleet, making Pearl Harbor its base