Yes, my downtube shifters are sturdy and dependable, but while climbing and bombing down hills, I just don't feel as comfortable reaching for the downtube. I was thinking of changing at least my rear shifter/derailleur setup to a newer Shimano 105 or something of the like. What all would I need? Shifter/brake lever, brake, cassette, AND derailleur? And what would be the cheapest possible way to do this? (I am a student strapped for cash!) Any help would be appreciated!