Problem with the dash instruments panel?

I've got a 1991 BMW 525i which has done 253,000 km. It's been a good car but, the instrument panel on the dashboard has gone silly over the past couple of weeks.
When I first start the car in the morning, nothing works - i.e. no fuel gauge, temperature gauge, no vacuum gauge, no speedo, no tach.
I drive for about 1 km and the euel, temperature and vacuum gauges start to flicker like crazy. Affter about 1 to 2 km they all start to work properly.
Then at about 2-3 km the speedo and tach go crazy. Sometimes they eventually settle down and work properly and sometimes at roughly 80-100 km they indicate I'm doing 20km per hour at 500 revs.
Sometimes when they've been doing this, if I stop the car and go to shops or whatever and return say 15 minutes later, everything works perfectly.
Sometimes, if start it on a hot afternoon, everything might work perfectly after about 500 metres or just go through its silly cycle all over again.
Any ideas and, will it likely be expensive to fix?