Automatic gear shifter gets stuck

What is your question?

With increasing frequency, the automatic gear shifter on my Lexus LS400 (1997) gets stuck in D3 and can't move up to N R or P (although it will move down to 2 and L). I have to just keep trying to move it up by going down and back up again until the shifter eventually moves pass D3. What could be the problem and how much will it set me back to fix it.