Trip Computer on Peugeot 307: problems with the trigger (b..

The button at the top of the lever, the switches among different
functions of the trip computer doesn't work anymore. The trip computer
works fine, but the trigger simply does not switch.
Since it is all "sealed", at Peugeot Assistance they told me they got
to change all the levers system (right and left one) by the steering
wheel...for an awful amount of 450 euro.
Can anyone give me a hint on how to work it out, without paying the
big ticket??
Many thanks