This is a good article from Bankrate about mold titled “12 tips for a mold-free home“. The fact is that every home has mold spores of some kind. The issues arise when the mold is the “bad” mold. From all the home inspectors I have worked with, the gist is this – remove the source of the water infiltration, and the mold problem will often sort itself out.

I have heard anecdotal evidence that having a radon mitigation system installed will help to dry out a basement — it may be worth it some some to have a mitigation system installed to work in conjunction with an always-recommended dehumidifier.

The EPA has some good resources on radon here, here and here, even a page specific to Virginia.

The cost of a contractor fixing a home generally ranges from $800 to $2,500, depending on the characteristics of the house and choice of radon reduction methods.  The average cost of a radon reduction system is about $1,200.
…  Systems that use fans are more effective in reducing radon levels; however, they will slightly increase your electric bill. The “Installation and Operating Cost Table” lists the installation and average operating costs for different radon reduction systems and describes the best use of each method.

Always do your due diligence and don’t be afraid to ask the “stupid questions.” Buying a house is a large investment, not just of money, but of emotion, time and peace of mind.