I have an old bike I bought off craigslist last summer. I love the bike, but it is now constantly misshifting, or sometimes the chain just pops off on me when I shift. When I bought it I took it to a LBS and had them tune it up for me. I'm trying to decide between buying a new bike from a retail store, saving up for a high-end bike from a bike shop or replacing the drive train on my current bike. Just looking for advice or input, and curious what I should expect to spend if I choose to replace my derailleurs and shifters. I'm not looking for anything fancy, but I'm 320lbs, and I don't know how bullet-proof of a system I need.
There is also the possibility that my hatred for friction shifting has to do with poor setup by the LBS I used.