2008 Toyota Corolla check light

The check light came on and I went to the dealer that I bought my car from. He looked it over and said 405.000 and I asked why so much. He gave me a paper with a code and I went home to think I went to toyota to ask questions of what was the code p0171 system to lean When I called the dealer the next day they told me it was the gasket to the manifold which is what the toyota person told me it should not cost 405.00 to elsewhere I went to my local repair man and he changed the filter on the manifold and the light went off. Then the light went on I went back to my local repair man and I asked him what did he do for 172.00 he said the if wasn't the gasket that was wrong I went to another toyota dealership and they ran the test and charged me 100.00 and said it was the gasket on the manifold.I spent 272.00 the light is off but who do I believe. HELP PLEASE