Snowplowing is pretty straight forward and there is very little overhead so I usually rent myself out at anywhere from $50.00 to $75.00 per hour for a regular sized pickup truck and driver.
If it's a small job I charge at the higher end because it is actually more work than a bigger job. A large lot (shopping center) means I will be there a while and I am not going anywhere wasting money on traveling from job to job so I usually charge $50.00 per hour.
Landscaping is the same except all my supplies are added on. All contracts are iffy. They are a risk. If you figure x amount of dollars for a snowplowing season and you get little snow, you make out. I it's a snowy season, you get burnt. That's why I use the hourly figure and send a monthly invoice.
Hope this helped:)