Starting from zero gear/experience, it cost me less than $2000.00 to get up and running.
-bike mods (service manual, sprockets, chain, petcock, oil change, adjust valves)
-tool kit with tubes, patches, etc.
-two day MC class
-helmet & goggles
I just did my first overnight trip this past weekend which included ~180 miles of dirt roads, 4x4 trails, and pavement.