First, you'll need to figure out your overhead :
Equipment and trucks being used, maintenance on them, fuel for them, etc. How much you pay yourself and/or employees per hour, Dumping fees, etc.
That should give you X amount of dollars per hour, what it costs you to work per hour.
Now add in your profit, what you want to make as a profit per hour.
Add those too together and thats how you charge!! Simple as that. You can price anyhting from mowing, to landscape jobs, to gutter cleaning (Bill's Favorite!!) All the same way as above!! People always ask how do I price this or that......its all the same method of figuring out your overhead and adding a profit.
For more in depth info on this method, check out Tips by Bill Phagen. He has some great books out, and is currently offering a discount for Lawnsite members. There is a link on my site if you don't have it already.
Hope this helps!!