Automatically re-numbering field on new item entry in Sharepoint list (SP 2010)

I am attempting to make a 'Priority Matrix' of tasking along with some contextual data. The idea is that each task would be given a unique priority from 1 to how ever many tasks are in the list.

Example list:

The trick here is that I need the priority to adjust for items lower on the list when a new, more important item is added. In the above, if a new priority 2 came up, I would want all priorities 2 or higher to automatically adjust down (e.g. 2 becomes 3, 3 becomes 4.)

For a more visceral example, if I go to Edit View, I am presented with the columns for my list and can reorder them accordingly. I would like to do the same for the priority field within the list. Alternatively, being able to reorder the list with a static field that identified from 1 to n for n items in the list displayed would also be fine.

I've searched pretty extensively without having any success. Thanks in advance for any help you can provide.