For a reasonable priced steel frame, check out Soma.
http://www.somafab.com/
I'm new to road cycling, and this steel bike is working well for me.
As for flex, I weigh around 190 and stand on the cranks all the time going up hills and never noticed any flex, the shifting works fine and no rubbing from the chain, the bike feels solid. I know one thing for sure, compared to aluminum, this bike rides smoother with less vibration, a very comfortable ride.
good luck...