1993 Toyota Camry slipped timing belt, caused by failed oil

At midnight, slight engine sound comes at same time as oil lamp light turns on (no flashlight in car, but manage to detect what I thought was no oil on dipstick, so I incrementally add 1, then 2, then 3 qts of oil. Only to my horror, on third quart, it goes down very slowly. So I figure I over filled it a lot--but it still drove the remaining 20 miles home. Oil lamp did not go off completely though. Flickered; a slight metal to metal sound is evident up to about 8-10 mph, then goes away even as I reach 50-60); next morning it starts up fine, with slight metal sound briefly, then it goes away again, then as I hit 20 slowly, nursing it up a grade, I gently attempt to accelerate to 25, and the tach hesitates, then drops to zero, with no sound whatsoever--just silently dies. Later, I see I have overfilled by appr 3 qts, so I drain the excess oil to normal levels. Car has all electrical power intact, as ignition attempts still to turn enging over, but it will not start. Local mechanic diagnosis slipped timing belt, by 4-5 teeth, and also implicates oil pump shaft (some how an oil pump shaft can break? Or fail? And cause belt to slip?); They want $1000 to fix the car, whose transmission has but 20K-30K left on it; a friend tells me (without ever actually looking at car) over-filling by 3 qts is what caused the belt to slip that far, and that the garage mechanic is lying about the oil pump center shaft breaking, just trying to earn some money unethically. Friend tells me max he could fix timing belt for $300. Risk of bent valve? Has me afraid to pour money into timing belt issue only to discover bent valve? What is your take on this