Promote/Demote Values

I'd like to see if this is possible without macros/vba, but I'm not even sure I would know where to start.

I've got a spreadsheet with a roster of names in col A and a priority number value in col b. I want to not only ensure a unique value in B, but automatically lower all of the other values in B if I enter a lower number. I'm using this to create a list to identify priority.
for example, my current table looks like this:

Smith 5
Jones 2
Williams 4
Doe 3
Johnson 1

What I want, is if I add a new entry and give him priority 1, that is drops Johnson to 2, Jones to 3, Doe to 4, etc. I'd like to do this automatically when the lower priority number is entered, not on open or on a button click or anything.

My first thought was to use drop-down lists for the priority and somehow (either formula or programatically) determine the non-unique value and change the rest of the fields. Any idea how this could work, either formulas or VBA?

Thanks!