Yes, $2-4K for portrait sessions is definitely possible -- that's not what I average, but there are pros out there who have minimum investments of this magnitude. If you can start attracting these kinds of clients, guess who they are going to refer? Their friends...who are likely to be in the same tax bracket.
Our experience was that once we started doing projection ordering sessions, our average sales number doubled. Our best sales session for a bride was $2,200 and for a high school senior $1,700. However it is not uncommon for our clients to reach the $1,000-$1300 range either. We call it the grand club, and probably 40% of our clients reach this. And when they do, we will throw in something extra (unadvertised) when we deliver their order, such as an accordion mini-album.
Starting in 2011 we are going to require a minimum investment after the session. Nothing extraordinary but enough to make sure that if we book a client, it will be worth our time. We have had some clients who end up spending more on the session than products.