If it helps, we just bought our first Prius last weekend from a Honda dealer. 2007 Touring with 114K miles. HV battery is original and service records were available left with the car by the 1st owner and on carfax. All Toyota service intervals had been done. Our price was $6200. I looked at a 2001 Prius IV with 124K at the Toyota dealer and they were firm at $9000. Based on pricing guides and research online, I was ok with my price. I don't know about other folk's experience, but I talked to two friends with Prii before closing the deal and they had original HV batteries and brakes at 190Kish each. I think the advice that's been given about looking into details of the service and why the brakes were done would be my first question.
I recommend you invest in a Prolong reconditioning system from Hybrid Automotive if you can afford it. It will help rejuvenate your battery to extend its life. @Raytheeagle and others here have seen excellent results from @jeff652 's products.
If you start maintaining the battery now, it should last you a long time. If you wait until the red triangle appears, it'll be a lot more involved to repair the pack and keep it usable.
Not sure what's going prices for 2007 in KC area but please do post your experiences after driving your PrII for about a year and see if it was worth every penny. You can always overpay at dealership. This is true when some dealers like Toyota/Honda/Subaru and so on even with used cars.