what's it worth? 05 Madone 5.2 SL

I'm going to make an offer on a friend's 05 Trek Madone 5.2 SL and wondering what you all thought it might be worth. This will be my first road bike, so other than way too many hours searching ebay and CL I don't really know the industry. The bike seems to be in good shape with low miles. It apperently has stock components for that year, all Ultegra. I've had it for a couple of weeks and I'm having a blast riding it, haven't been fit but it feels good (and scary fast) I also know that she got a killer deal on it a few years ago and it was just collecting dust in her garage.

Thanks in advance for any input..