The EA-6B wouldn't make a great sim program, as it's almost always unarmed and does nothing except fly in circles and jam radars.
I don't know about any Harrier study sims, but the best Harrier modeling I've found is in Jane's "Fighters Anthology". You can also fly the EA-6B in non-campaign missions, I believe.
"FA" costs about $15 at CompUSA, Circuit City, and Best Buy. It can also be found at Electronics Boutique or Babbage's once in a while.