First off, you should have posted this in the B14 section, but you have a couple options in this case. One of them being you can replace the entire cluster, or you can go for an aftermarket tach that you mount on your dash.
You can replace just the tach and it's less than $50. I recently converted my 98 sentra w/ no tach to w/ tach. Mines was a bit cheaper. E-mail me and I'll send you to the right place.