When attempting to determine Challenge rating, a few things are to be considered:

1. How difficult do you think this monster should be to defeat for a single person?

Keep in mind that a level 3 character vs a single CR 3 monster is considered a "very difficult" encounter.

2. The "Dire" template adds +1 to that challenge rating.

3. I'm way too much of a nerd for this kind of stuff

This is a critter that is nasty if it gets surprise but would be easily handled with missile weapons if spotted from a distance. Could go either way. 83