I spent 7500 getting my private in a little over 40 hours, but that was at a part 141 school. The idea that it will take close to 10000 for a private part 61 is just plain stupid. The only people who I know who took more than 60 hours to get their private were stoners, so I guess that does explain a lot. The amount of time spent studying and flying as often as possible (2-3 times a week minimum) is inversely proportional to the amount of money spent getting a private (but one must as well factor in lurking variables as mentioned above).
Anyways, back to the original idea. Like others have said, a private will not hurt, but it is not required. The questions I remember seeing based off aviation areas where not very in depth. From my experience as a CFI I think buying the Gleim's Private Pilot FAA Knowledge Test guide will get the job done. If you can pass the FAA written you should be able to do just fine on the ASTB. The information asked on the ASTB would fall under the lines of listing the types of flaps, reasoning behind runway numbering and airport light configurations (but this was my test so it can involve different information). Also, read every thread under the ASTB section on Airwarriors and download every guide/gouge.