This all depends on several factors.
1. What is the power consumption? Here in Denver, electricity is $.0445/KWH (I think).
Running a 1500Watt (1.5KW) heater - or any 1500W residential load, for that matter) 24/7 for a month in Denver is roughly $50.
2. Oil filled means that the heat is not necessarily directional (but as the above post points out, heat rises). This is different than the heaters with the cones that direct the radiant form of heat directly at you and you lose the benefit as soon as you move out of the parabola.
3. Room size, insulating factors, solar gain, wind loss, room direction, i.e. heat loss factors are simply incontrovertible parts of the equation regarding satisfaction.
4. Objectively, if you use it to increase the comfort level in an area of frequent habitation, while keeping the balance of the rooms at a less than comfortable level, this unit will eventually pay for itself with the differential.
However, all other factors being equal, raising the temperature with this unit in one area of the domicile while leaving all the other areas the same will cause your heat bill to rise, be it on the gas side of the bill or the electric.