2000 Mercury Sable oil light

I have a 2000 mercury sable. The oil light is flashing when idling after the engine gets warm. I took it to the dealer they charged me 172.00 to investigate and put in a new sensor. They said the 2000rpm pressure was 45 but the idle oil pressure was 5. They said they would have to drop the pan and it could be 1 or 3 things wrong or all three. Something about replace bearings. The car has 126.000 miles I have kept it up with oil changes every 3-4000 miles. How much would it cost to get this fixed? I was told to basically its not worth it. The best bet is to run 10w40 and then stp additive and see if that will keep the pressure up at low rpm. I would like to get it fixed I have sunk 850.00 into it last week in struts and springs and hubs. The studs for the rear passenger all broke off but one and on the drivers one broke off when they were taking the wheel off. Also I just put 220.00 into new brakes on the front rotors and pads. They said I will soon need out tie rods there is some play in the passenger one. Is it worth it to fix it? I have a daughter that will be 16 in 2009 she can drive it hopefully just around town if I keep it. If you think its worth fixing how do I find a decent mechanic to do a good job at a fair price? They want to charge 400 dollars for 2 tie rod ends not counting a wheel alignment.