How can I find parts and labor costs for repairs?

An estimate for the PCM is tough because it is generally not the labor that is expensive, it is the wide range of prices of the PCU itself. You can get them re-manufactured, with a warranty, or you can get a new one however the cost would be extremely high. You could take a chance and get a salvage PCU. Some of the better salvage companies will give you a short warranty to at least see if it works when you put it in. Use the search engine on this site to look for PCM retailers. You will note that any mention of PCMs in the search bar will bring up ads and ad banners on the page you get sent to. They are all credible as we do not deal with any retailers who have a history of inadequate service. So, the labor will be on ht elower side, probably less than an hour, but you will have to call to get a quote on a PCM. You can also do your own web research. If you should ever need parts, there is a site under development called carrepairlinks. Com that has brought together the most reputable and best customer service oriented, and other criteria to make searching for a parts retailer online easier as the experience of dealing with the retailers is already been done on a long term basis and you will have a good place to find parts if needed.
The important thing to know when getting an estimate is the hours of labor to repair. This is because repair shops vary. Independant shopos, this also depends on where you live, might run $70 per hour while a dealership might be $100+ per hour. The throttle position sensor $200, (at a independant repair facility) and $500, (at a dealership). The time time repair is an hour. The Mass Air Flow sensor will run $300 to $400, these estimates are to replace said part. An O2 Sensor will run $200 to $300. The lean reading could be false could be an exhaust leak near the O2 sensor letting oxygen in and giving the lean reading. Welding the exhaust would depend on the extent of damamge.
I hope this information helps.