Having an adventure for under $2500 isn't even a challenge.
I bought my '82 CB900C for $1250, put about $250 in parts to make it run, paid $100 for a Windjammer, paid zero for a KG trunk, got a set of used-only-once Nelson-Rigg CL-850 saddlebags for $25.
30,000+ miles later, I'm still enjoying every minute of riding it. In fact, I'm entertaining the idea of taking it to Chile next year.
(Since this picture was taken, the trunk has been replaced with a Vetter trunk. Still way under $2500.)