I spent $1,100 on a GeekDesk max (including shipping). An investment in my health was long overdue, especially since I've spent $4-5,000 on my computer setup. The huge benefit is not having to move all your stuff whenever you're done sitting or standing. I press a button and in 10 seconds it's changed height. MAGIC! I highly suggest them to anyone, just watch out for the long backorder. Mine took 3 months to get here…
I just got my GeekDesk after a long and varied string of various sit/stand combinations. I opted for the small, frame only, and bought my own "butchers block" solid mape top - 48" x 25" x 1.5". This coupled with an ergotron LX monitor mount and a humanscale keyboard tray is beyond fantastic. I can adjust everything, and I love it.
All in all, it probably set me back about $1000 (including the keyboard-tray and monitor-mount). And it was worth every penny; I'm much more comfortable after long hacking sessions.
[1] http://imgur.com/4XGYh [2] http://www.ikea.com/us/en/catalog/products/60057852/#/200578...