Any Arduino will do (Uno compatible / ATMega328 chip) and then you also need an ethernet shield, preferably one with a Wiznet W5100 chip. Combined the two should be less than $40. You can find lots of examples of how to serve a web page if you do a little searching.To read your voltage you just need a couple resistors. If you have any interest in electronics you should buy an assortment pack of resistors, but if you just want to do this one project then a 10K potentiometer or seven 2200 ohm resistors would work (when combined to form a 8800 and 6600 ohm resistance). http://fritzing.org/projects/voltage-divider/ for an example.