Sora absolutely works fine but most people absolutely HATE the thumbshifter. I've never heard anyone say what you said about a 105rd being so much better than a sora. Sora RD works fine but if you crash, it's toast because it's all plastic. Consider microshift brifters if you really want sti at a good price point. I have them on 2 of my bikes and they are excellent. NAshbar has the 10speed version and usually on ebay you can find the 9speed version if you prefer a 9speed. i find 9speed casettes/chains, etc to be cheaper to replace.

https://www.nashbar.com/webapp/wcs/s...ey=http:Logoff

There is also a nashbar microshift RD available. I have the MTB version on my commuter and it works great and looks better than the pics of it.