It costs what it costs... in your are I'd think you'd have more than one certified independent lab. Check with county or state Environmental Health Departments to see if they can point you to a couple labs. Check and see if a local university provides lab services.

Check for hardness, iron, manganese, sodium, chlorides, TDS, PH bacteria, and nitrates at a minimum. You really should be checking bacteria and nitrates annually. I'd get all those tested on the water BEFORE the softener.

For softener peace of mind hardness, iron, manganese, TDS, and PH need be tested on the treated water IF there are no nitrates and/or bacteria in the raw water.

If the only lab test you had done on a well was by a softener seller then you may be surprised to see independent lab results.

Google is our friend...

http://www.mass.gov/dep/service/compliance/wespub02.htm