#1 take a course. I did TooCoolMotorcycleSchool - they were great!
http://www.toocoolmotorcycleschool.com/
#2 really - take a course. Major differences are that a bike can react way faster to stuff (turning, breaking, accelerating) and that you need to elevate your defensive driving game because cars often don't see you. Look for guys going to change lanes over you, cars making a left in front of you etc. It becomes 2nd nature pretty quick to spot dangerous situations, but doing a course really helps for this
As for bikes and prices - you can spent anywhere from $4k for a decent used bike on kijiji to $25k on a brand new Ducati. What kind do you like the look of and what kind of riding do you want to do? Crotch rockets vs. cruisers vs. sport touring? Pretty different recommendations depending on what you want to start off with.
Insurance was about the same I remember (had kids, had to get rid of the bike).....liability is way less (you're likely just going to kill yourself on a bike) but comprehensive was way more as they can get stolen and are easy to write off (been there, done that).