arduino 250 input lines demultiplexer and sensors

This project consists of 3 parts. one freelancer can provide a solution to either one of the parts, or two or all three, depending on your skills. The solution should be easily scalable without adding more complexity to the design. Part 1. I need to choose reliable sensors to detect if there is anything in a drawer. I tried motion sensors and they proved to be unreliable when they miss the moment of a short motion. I tried light sensors but they proved to be unreliable because when some drawers have vent holes in them and the light from the outside triggers them even when nothing is put there. This time I am thinking of having a pair of LED (either in visible spectrum or infrared or something lese) and a light sensor. I am looking for a cheaper solution, easily scalable to 250 drawers and the most reliable. Part 2. I am looking to make the simplest possible demultiplexer to take 250 inputs into one arduino unit. There is very low demand on real time processing. I don't need all 250 lines to be monitored at the same time. I can poll the state of every input one at a time, maybe once every few minutes. I don't want all LEDs to be lit all the time. Ideally I would like to light one LED at a time, when i read a light sensor associated with that LED. If the state has changed (or if this is the first polling after arduino was restarted) - see PART 3 of the project. If the state has not changed - do nothing and move on to the next one. Part 3. Software support. I need arduino to poll each of the 250 inputs consequently, one at a time and compare its state to the previous state. If the state has changed i need info about it to be sent over the internet to a server. It can include authentication info, for example user name and password, Arduino Unit ID (in case if we have mor ethan one 250-input units), drawer ID (input number), Current state and maybe date and timestamp. It can send info to a web service or as XML file or upload as a file to an FTP or just a specially formed URL with everything encoded in it. Ideally everything encrypted (but encryption is not a firm requirement). Maybe a good idea to have a variable to set the time interval between polling each input or do all of them and set up a delay interval between full polling cycles. I might have less than 250 inputs at one location. But the solution should work pretty much the same way and be easily scalable to use as many unputs as i need, up to 250, without excessive hardware and electronic components. The less wires the better.