You can get $150/hr for a Bobcat and mulcher... I'd be looking at $200+hr. for a dedicated machine like the 140. Your haul costs are going to be higher as are your fuel, maintenance, etc. While you may not be as versatile, on a straight mulching job, you will mostly out-cut a stock skid steer or CTL so charge accordingly.
Part of my pricing strategy is versatility. I ask a little more than some of my competitors but I have a lot of attachments and a few extra years of experience. Not every customer is willing to trust that my experience or extra tools are worth it and that's fine but I refuse to work my setup for the prices that some guys are charging for an old landtamer on a worn out skid steer.
I think once you know your fuel and maintenance costs, haul costs, etc., you can start to justify your price per hour. Of course, the demand for your services plays into that pricing structure. When the burn bans are on, you might get a little more per hour. Personally, I've just stayed consistent for the last 4 years but it's looking more and more like I need to have a delivery fee or go up on my price per hour. I'm still thinking about it.