Need to buy cheap bike. have no clue

Ill be going into the military in 3 months and im looking to buy a bike that is good for exercise and park trails. i have no clue on what to buy because ive personally never bought a bike. there is no way in hell im paying over $200 for a small piece of aluminum with wheels. i dont understand these bikes going for $500+. personally id buy a motorcycle if i had that kind of cash.
im 6 foot 4 so the bike needs to be larger. a hybrid mountain/road would be nice. meaning i want shock coils but not huge fat tires and a super heavy mountain bike. help would be much appreciated.

For what it's worth...

For those of you interested, here is the e-mail I sent Phil Williams (he's very responsive), and underneath I will post the reply I had from him (yes I asked his permission to post it).
My e-mail to him:
While in office, one of the things I hope you could change is the State's stance on obesity, fuel conservation, and cheap transport for the citizens of Alabama. One of the things that stands in the way of all of the above is Alabama's laws concerning motor assisted bicycles which defines any modification to a bicycle such that it is powered by something other than human power to be a motorcycle and thereby subject to all the laws of a motorcycle (turn signals, obtaining a VIN, DOT approved tires, license, etc)