Rotting Floors and Mold in Crawl Space
It is also impossible to give you an accurate assessment of how much it will cost over the Internet because we have not seen the house and do not know what contractors in your area charge. Because you plan to hire it out, you should definitely consult with contractors in your area BEFORE purchasing it so as to get a more accurate sense of how much it will cost to replace.
Mold is the asbestos-fad of the turn of the millenium, hyped by trial attorneys and sensationalist media types. The hype around it contains many false rumors, exaggerations, and outright lies. Mold has existed for centuries in homes, but only recently have people made inflated claims that it is "toxic" and lethal. In the most rare, extreme cases, you find the rare, dangerous types of mold or the ordinary mold can get so bad that it poses a serious health hazard. But mold usually is little more than a foul smell that can be eliminated through routine cleaning (with bleach) and air filtration/circulation.
That said, mold definitely is not a good thing to have in a home. Mold can contribute to respitory problems in people with allegies or athsma. I recently put my new home through a gut rehab, in part to find the source of the mold smell because I have asthsma. I ended up tearing down several walls to find all the mold. The main source was in the A/C plenum because of a leak and the fact that the A/C was turned off for months, allowing the mold to grow. That same leak allowed mold to grow in the walls, on the studs, etc.
The only thing that eliminates mold and its spores completely is bleach. I treated the studs with bleach, painted them with mold-resistant paint, and put up new drywall. (I also did other renovations inside the walls, including plumbing and electrical work, so it was not exclusively to eliminate mold... more of a "while I'm in here" type of endeavor.)
You can also use ultraviolet radiation or dehumidifiers to kill mold. Mold evoloved to thrive without sunlight, but it still needs moisture/high humidity to thrive. If you expose it to UV light or dehumidify the area, you will kill the existing mold, but the spores will remain to develop if darkness and humidity ever return to that area. You can dehumidify with a dehumidifier or with chemicals similar to the chemicals in those small packets you find in clothing or foods.
If your problem is severe, you can expect to need to rip down some walls to kill the existing mold by applying bleach to it. If it is only in the crawl space, though, you can just douse it with bleach, place a UV lamp in there for a while to kill what remains, and de-humidify it. A dehumidifier in the home for a few weeks also will help to eliminate the humidity that mold needs to thrive.
Mold can also contribute to weakening studs and structural support, but that is usually accompanied by wood rot from the same moisture/ high humidity in which molds thrives, not from the mold, itself. When a home is burned down due to mold, it is because the home is not worth much, to begin with, such that the cost of renovation to eliminate the mold exceeds the value of the home.
[This message has been edited by Lawrence (edited February 19, 2003).]