An 1/8th will last me 2 to 3 months, sys, with an average of smoking around 3 times a week.
Legal prices are pretty comparable. prices are fluid obviously, but back in January I got two 1/16ths of "top shelf" quality for $55 total, taxes included. Erii can maybe give you a more recent number.
As far as smoking in public legally, that's a problem they are attempting to solve right now. I believe a few counties have authorized smoking patios at bars, not sure if this has made it to denver yet.