What bike would you start out on?

I recommend not going for any late model 600's. These are essentially track bikes and all of them have on/off torque curves and relatively high seats. An early '90's or earlier model would probably be ok.

Other than that, most have already pointed you in the right direction with the SV and Ninja 250/500.

Also try to keep in mind what type of riding you'll be doing. Unfortunately, many people buy bikes that are not well suited for their riding. Of course, the end decision is always the buyer's but I think buying an R1 to cruise on the street is overrated. An SV or Monster has more performance than any rider could possibly use on the street and is much more ergonomically friendly.

Here's some of what can be done to a Ducati Monster.
http://ducatimonsterforum.org/index.php?topic=32135.0
Here's the wifes 620.
http://ducatimonsterforum.org/index.php?topic=28634.0

I admit it, I have a slight bias about european machinery