A will does not take effect until it is filed for and admitted to probate. She should do it, assuming there was anything in his estate of value, or land in his name only. If everything was in joint tenancy, or insurance, there might not be a need to file as nothing would pass under the will.
As to what it costs, it depends on the size of the estate and the amount of time it takes to do the work. If he had nothing of value and it need not be probated, or if he put everything in a Living Trust it would take no time.
You should always ask the lawyer what it costs and at least get a ball park estimate. Lawyers often charge from $100 - $400 per hour for their work on estates. Ask a local lawyer on AttorneyPages.com.