Auto Populate Fields

I admit I'm relatively new to Access and even newer with SQL. I have a table called Benefits that has a field named Plan and a field named Status.
I want to write a query where a new field Cost will auto populate based on the info in Plan and Status.
Example:
If Plan = 1 and Status = E then Cost = 100
If Plan =1 and Status = ES then Cost = 150
If Plan = 2 and Status = E then Cost = 125
If Plan = 2 and Status = ES then Cost = 175

Plan field can only have a 1, 2, or 3 in it
The status field has 5 different potential answers in it.

I appreciate any help I can get and someday...when I get good at this...I'll give back!