I managed to find more information on the brighton badge, I can see where you got the idea to merge everything but there are some serious flaws in what you came up thinking. The brighton badge uses a IR detector like in remotes and such, thats OK but not needed, there are cheaper and better sensor's, the remote one is also too directional.
What you want is a flat sensor like a SMD one, while the pick up angle is that much greater somehow it does make a difference.
The main problem you have is the BB (Brighton badge) dosnt collect information, I havnt seen the source code but I imagine it simply pumps out a signal and waits a response, then on getting a response software decides what colour to display.
Any small micro will do this kind of thing, what your after is the distribution and collection of data. Straight away you have to then add in storage for both the user's data and the collected data, most micro's come with eeprom so that would seem easy enough, however you want 500 badges! say you just had 100 different badges in a room, how long is it going to take to fill 250K
of eeprom space? not long!
So your looking at external storage, micro SD looks ok at first glance but gives you collection trouble, you have to get hold of each card each day or at the end, also cost, You need to decide if the PCB is the badge or if you want a PCB inside ready made badge? Both come with there own problems, a ready made badge means you have to find then alter a ready made badge, add to that the need to fit a battery and it gets clumsy. The obvious way is a custom built plastic badge case, but forget it for 500, the set up and tooling cost's make it a massively expensive badge.
So you could go the PCB is the badge route, this is fine and probably your best option, but then you need to consider aesthetic design of the circuit, not only does the circuit need to look good but has to be weight balanced as well, two reason's for this.
1) if its heavy at any one point it wont beam data in the correct direction, heavy at the top and it may beam down at peoples shoes! also unbalanced will pull on the clip/safety pin, this could damage clothes!! non of this is going to make you or company look professional.
For $30 you can get a pre built answer with a LCD but again thats just for the hardware, these things are made high volume and sold by a certain silicon manufacture as badges, getting 500 at once though would be a challenge and then you are going to need to alter it anyway.
So we are back to square one
FORGET the DEFCON badge, nowhere have I found a hint of the cost but I can tell you a couple of things about it. There was no design charge, the people wanting it designed it and they programed it, so all major dev cost's were covered. This means if you could get your badge on budget, IF you could do it yourself. So without being rude but without wasting time can you do this on your own?
No, because 1) your here and 2) I doubt you have the time
Does that mean it cant be done? No it dosnt, but I suggest you get some answer's for the earlier posts so we can get you on the path to salvation and all things electronic.
Next year seems a long time away and you maybe think you have time to go looking around, maybe even look until say 6 months before you need them. Please dont do this, I have given this alot of thought and while I dont have every answer yet (you havnt answered my questions yet), I can tell you that this is not a time friendly project, get it wrong and you do more harm than good, The PCB as a badge will need a good deal of messing with to get both the balance and look right, and get it to work. But I think depending on what your company expect to achieve at these conferences, you could well be on to a good idea. The badge for $30 with LCD last's for 3-4 days on a single 90 second charge from a usb port, while you wont get anything like that, it does show that 4 days from a small battery, is doable if done correctly.
I will await some answer's to previous question's before I can do much more, I did look into IRDA for you and it isnt needed, there is a more simple way to do it