I'm trying to figure out the most effective approach (chemical vs heat vs cold vs fumigation, etc).  

It ultimately depends on the individual buyer and their personal beliefs and concerns.Regarding a property that was once used as a meth lab or for illicit drug use, it's important to note that these properties can present significant health and safety risks due to the chemicals and residues involved.

My local health dept and our local EPA has been in the back pockets of big business allowing them to dump toxic chemicals into our rivers and leach agent in our back yards for over 20 years, all while they want to soak the little home owner who is simply trying to sell his house and move to a better life.

I am a 21 year old rising senior pursuing a chemical engineering degree.

.: manufacturing or distributing illegal substances, storing, manufacturing, or selling explosives, flammables, or other inherently dangerous substances, chemicals, or unlawful devices)."

I think I know the building and there is not much to consider with this type of use: if chemicals were used your lender might require a phase one envirmonmentals study, but I don't think that's the case here.Issue number 2 is that it can take a while to find a new commercial tenant, so while tenants typically stay a very long time, if you have a turn over you may have to spend some money on preparing the space for a different use and it could be some time before you have a new business.

The plumber quoted $900 to jet it out, or $3500 to dig up and replace the pipe.I see there are chemical root treatment options for this that is much cheaper.  

Chemical treatments can mask smells, for awhile.Fire restoration is a specialty and I'll bet the inspectors will be very tough on a new guy breaking into the business.

It's nasty, hot/cold work in confined spaces, heights, noise, chemical pollution, etc. 

He's a mad scientist with water temp, soak time, the chemicals etc.