Some students (mine for example) have a good idea about what their income needs to cover (rent, food, transport, etc), and what those things cost in their home town, but not what the costs are where their future employment is. For instance, our S was pricing apartments in a SV locale and was floored at the monthly rent for a studio apartment. Floored as in finding out that the monthly rent for 800 sf apartment was more than the mortgage for our 3,900 sf home (with a diving pool, spa, and basketball court).
The tax estimation web site mentioned earlier is handy. Wish there was something similar to estimate total cost of living for a given area. There are some that compare what it will cost you to live in a new area based on where you currently live. But none just list what it will cost for a new grad to live in a new area.