Bayonetta on normal took me about 10 hours or so (I think when you factor out the parts that I had to repeat about a dozen times). If you want the full 1000, you are going to need to play through it at least 3 times though, as you need to unlock the harder difficulties. I have the hard playthrough on my list of things to do over the holidays.
I would recommend trying to find it cheap rather than gameflying, since it can be pretty tough at times and owning it will allow you to play at your own pace. I think I saw it new for $25 up here. If you can find it for under $20, it would be a reasonable deal.
Oh, the game is cake, the big thing is that in relation to the rest of the game, the time trials are very hard. I think it took me an hour to mop up the hard time trials (the egg rolling courses and the flight sim level), bringing it to about a 5 hour 1000. Nothing significant. The problem with the egg rolling is the lack of a margin for error, you need to do things exactly right, which isn't tough, just annoying.