You might be getting something what we call "blow by." You rings aren't sealing anymore and it's letting oil from the crankcase get into the combustion chamber, there for.... "burning oil." Are you smoking at all? take off that little hose off the nipple on top of the valve cover. If at idle, your getting smoke then you need to replace your rings (probably pistions as well).

if you pull the engine and give a shop the bottom end, the rebuild will cost 500-800.