Where do you live? I'd try several different bikes across several different styles and brands to see what feels the best when riding it. It probably wouldn't hurt to go to more than one LBS, as often, each LBS specializes in only a few brands.

When you're off-road, what kind of paths will you be on? Bike Trails that are still asphalt? Hard packed gravel? Loose Gravel? Mountain bike trails? The one you mentioned is a mountain bike, so it won't be as good for you as a hybrid or road bike when you're doing 80% of your biking.

Is $800 the budget for just the bike, or for the bikes and all of the other biking equipment (e.g. helmet, bike shorts, gloves, tire repair kit, etc.)?

I recently got a $800 bike from Performance Bicycles (Fuji Sportif 1.3 C - 2014), and it's a pretty big chain of bicycle stores, so there may be one near you. It has 28/32 spokes per wheel (front/rear), so it can handle bigger guys like us. I'm 5'5 and ~250#. I've been happy with the service at my local Performance store. I'm still in the beginning stages of riding the bike, as I'm old, fat, and out of shape, but I figure by getting back into biking I can do something about 2 of those 3 items.

GH