I went from Sora to 105 (5800: 50/34, 12-25) via eBay. I pieced together a complete groupset made up of take-offs and new parts. A week's worth of effort made it cost about $350...then a few days later I saw a complete set in-a-box for $400. I don't regret doing it the way that I did but if I could do it over again, I'd get the box set. The real kick in the nuts was the cost of the tools...those Park tools arent' cheap--even on eBay (only bought new tools). I bought some Mavic Open Elite wheels from eBay to complete the conversion. Damn project cost me $600 but it was a fun and I'll be keeping my Allez Sport until I die now.