I have a '96 Contour GL v6 automatic that just flipped 100,000 miles. My CEL is on and has been off and on almost since I got it. First I was told it was a vacuum leak and got it fixed....light came back on after three weeks. Then I was told it was an o2 sensor, but couldn't get an appt. to fix right away and was told it was ok. Now, I'm trying to get it fixed and I need to go through emissions testing and I won't pass with the light on

I paid some idiot mechanic $85 to read the codes, ended up being $145 "for diagnostic" and he couln't figure out what's wrong.
I took it to AutoZone, and here are the codes:
P0430
P1151
P0171
P0174
I don't have the knowledge to fix it myself, nor the money to pay a lot for someone else. I'm hoping for some input where to start...
Thanks,
Kristin