Where to find an AED at a decent price

I live in Indiana and yesterday there was some freezing rain.  I was driving to work and there was a terrible accident. Being a good Samaritan, I stopped my car and got out to see if I could help.  Two other men had already gotten the driver out of the car.  The driver looked to be in bad condition.  One of the men ran to his car and brought back with him this odd looking machine.  Before I knew it he had told the other man to get back and yelled “Clear.”  It was a mini defibrillator!  I never knew that people could have their own AED, automated external defibrillator.  Where do you buy one of those?