1999 Jeep Cherokee Oil gage randomly goes to 0 when at idle

I have taken the jeep to the deal and was told they prefer to wait until the guage or whatever fails befor they will inspect or replace anything related to the oil pressure guage.

Where is the oil pressure sending unit?
Can I remove and replace it without too many special tools? Will I need a special tool?
Generally, what is the cost for a sending unit for a 1999 Jeep Cherokee Limited?