Hello. Welcome to Just Answer. Please allow me to assist you. Most often, oil consumption comes form one of the following:
1) Seized oil control piston rings (carbon builds up and the rins do not orbit the piston as it reciprocates. This causes the ring to not scrape the oil off of the piston walls
2) Worn out, hardened or other issues with the valev seals (oil tends to make the valve seals less pliable. This causes lubrication oil to trickle down the stems o of the intake valves and into the combustion chamber where it is consumed and then spent out the tailpipe.l
3) Sludge (sludge buildup can congregate into the valve covers. When the PCV system activates, the trapped oil that is on top of the sludge actually gets sucked into the intake manifold via the PCV system, where it enters the combustion chambers and is consumed.
The first thing to ask them to do is pull the valve covers and check for sludge. If sludge is found, you are looking at a lot of money to clean it out. Include replacement valve covers (the cannot be cleaned properly manually), and there would be a high probability of needing piston rings.
It would not be uncommon for a shop to charge 7,500 dollars for a complete cleaning and replacement of the rings and valve seals.