95 pickup with no reverse

I have a 95 Nissan 2WD (manual). Going into reverse, there use to be a clunking noise all the time. Before I got a chance to do anything about it, this problem evolved into me not being able to go into reverse at all. I go into gear and when I release the clutch you hear a loud pop and my truck jumps out of gear. Should I invest in a new transmission, do I just need a synchro or a gears? Obviously I dont know much about this. I work a lot, weekends are about the only time I have. Is this a possible weekend job or longer?