I had a Pioneer head unit in my 97 EX and had the stock unit shoved behind the dash just like you've got yours now. You should be able to get a pair at the Honda dealer for that $80 bucks. If you ask for one sometimes they'll just sell you one for $80, but two come in a box, so you should get both of them. I had to replace mine after it died, and was told that I could either get one for $80 or two for $80. I bought the pair, obviously, and sold the other on eBay and got some of my money back (only like $20 or so, but still, better than nothing).
Anyway, they'll come with instructions on how to reprogram the remotes. There's a button on the front of the stock headunit that you DO have to press and hold while yuo do stuff with the remote. When I reprogrammed mine, I just had to take my lower dash off and pull the stock head unit out enough to push that button, then shoved it back in when I was done. You'll have to do this every time you have to reprogram your remote and it's a pain in the ass.
With the deck being back there, the only wires you NEED connected to it are the constant power and ground wires. If you don't have those babies hooked up, the keyless won't work.
I didn't see any loss of range when I stuffed mine in my dash. I should still unlock and lock the car from about 100 yards away... unlocking it from my apartment while it was sitting in the parking lot wasn't a problem through the window, and that's atleast a good 50 yards or so. If the signal can go through the metal body of the car, going through a plastic dash isn't really an issue.
