Engine oil consumption can only be caused by a leak or the engine burning the oil. A leak will be obvious as it will leave oil under the car where you park or oil film on the engine. Oil burning internally in the engine can be due to the oil control rings, cylinder wear, valve guide or valve guide seal wear. Try changing up one viscosity of oil say go from a 5/30W to a 10/30W oil. If any of the spark plugs show signs of fouling the problem will need to be addressed. Fixing any internal problem is going to be more expensive. The cheapest item you can replace is the PCV valve in hopes this may help, it controls the way the engine breathes and recycles oil vapor.