The Benchmade 585 Mini-Barrage is usually more expensive than the mini-griptilian. The $65 tag is a good price especially since you can send the knife to Benchmade and they will sharpen/clean/replace-parts for free.
The mini-grip is an "entry" benchmade knife - it's been around for quite a while, is among their least expensive offerings with the AXIS-lock, and is available in a variety of colors/blade styles.
In terms of differences, I own a 585 and not a mini-grip because i could not well hold onto the mini-grip - it is quite "mini" (image pulled from web):
The mini-grip handle is very small, fits 2 or 3 fingers unless your hands are quite small, while the mini-barrage fits 3 or 4. I prefer the blade-shape of the mini-barrage. The assisted-opening is strong and smooth (MUCH better than a torsion-bar) but still easy to close the knife one-handed, and the safety-switch works well to lock the blade closed or opened (a bonus should your omega-springs ever fail). The mini-barrage can be de-assisted to function as a manual (mine currently is), there are youtube videos of the process.
The 585 liners are skeletonized to reduce weight, but this along with the hollow sound of the plastic handles (which are a bit slick) make the knife feel "cheap" to some, though it remains strong and lighter than it is with G10 (also available).