House costs are in server up time. Every hour that the server is up, an hour of maint ticks off reguardless of whether your logged in playing or not. When the servers are down, there are no maint fees for houses, harvesters, or vendors.
Vehicles do not have maint cost. They have durability, "hit points", and repair costs. Your vehicle takes damage when you generate it, and for every "tick" that it's out. They also seem to take more damage when you run into buildings, etc. When your vehicle needs to be repaired, you must take it to/ generate it at a garage, and select "repair" from the radial menu. (Garage's are located in the main citys... they look like an open building with a ramp leading to a couple bays.) Vehicles do not take damage when they are stored in your data pad (or when your offline).
If your short on funds and worried about vehicle maintance costs, get a creature mount for your ride instead. For non-ch a carrian spat or kaadu is a good choice. They aren't quite as fast, but they will slowly heal on their own, and only take damage if they get in a fight.