Rav 4 key fob stopped working?

I have a rav 4 (1996 model) and recently my key fob to unlock/lock the
car and turn on alarm and immobilser has stopped working. Basically I
opened the car with it then went to lock it and it wouldnt work. I have
replaced the battery and this hasnt resolved the problem. The little
red LED light comes on OK. It is the black rectangular fob with one red
and one black button. When we bought the car two months ago we also got
a second spare key. The fob on this has never worked which leads us to
believe that it is a problem with the fobs and not something with the
car. Anyone have any ideas for a fix or will I have to take it to the
dealer and shell out what my mechanic tells me will be =A380 or =A390?
Many thanks for any help
D