okay, the A/F meter is around 200$-300$ at the stealership, order it from toyota of dallas for the cheapest price i know of.
in order to replace it, you simply wait till your exhaust is cool, spray some pb blaster on the bung/nut, go inside, watch a tv show or drink a beer or two go back outside and remove the old one and insert the new one. REAL EASY TO DO, if you can change a tire you can change your AF/O2 sensors
if you want to clean your maf thats also easy to do (if you have a 98?99 or up with the newer maf that is only two screws to remove (be careful they strip easily) you go buy a 5$ bottle of electronic cleaner from the auto parts store and spray it in liberally until you get all the "gunk" off the sensor, let it dry all they way and reinstall.
a dealership or other shop will prob charge you 5-600$ to do these simple things that shouldnt take you more than an hour (with the beer drinking) and less than 300$
its really stupid simple, no reason to waste a couple hundred on something you can do yourself