I think it depends on how well the last rewire was done in the 1980s.
If you still have 'original rubber' cable then a rewire will need doing sooner or later - as the rubber will perish.
Also PVC cable is normally thought to be OK for 25 years, it can last longer, but sometimes it becomes brittle.
Moreover, Electrical regulations now require that an RCD (residual current device) - a type of safty trip fuse should be used on each circuit. A house rewired in the 1980s probably won't have this type of fuseboard.
Also, nowadays some appliances need cable that can handle greater amps (power) than was probably put in during the last rewire - for example storage heater.
Cost would be dependent on the size of the house and how much work needs to be done. Also costs might include replastering and redecoration (most electricians will cut channels in the walls to feed new cable to sockets). A rewire really dose make an enormouse mess.
My 1950s 3 bed semi cost £4000 to rewire, including some dodgy plastering and no redecoration - I did this part myself.