po171 and 174 are lean codes bank 1 & 2 and po300 is random misfire code. where did you get your description on codes because they are wrong. you could have a lerge vac leak or several other issues seek diag and est from your mech
Global helper is saying that NO ONE can give you a proper estimate on price and repair because EVEN
YOU don't know what your codes mean on your car! It is impossible to tell you what is wrong with your car just based on codes you interpet an inspection report! He is right, GO to a shop and spend the money to get a proper diagnosis and estimate for repair!
(if you believe anyone stupid enough to give you a diagnosis and estimate by your "say so" in this situation...then by all means, GO FOR IT! and good luck...you'll need it!)