Any other thoughts? I should go forward with a prebuy, correct? Ballpark, what would that cost me?
I forewent the pre-buy, and just had an annual done. Cost=$1,100... in western North Carolina, circa 2006. To answer your question further................, It depends.
When was the last annual done?, What is your comfort level in just getting a "pre-buy" inspection, and how badly do you just want to get the plane out of there! Maybe, You've struck a good deal, and you just need to get it home?(fly it like you stole it!

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I think a pre-buy would typically run about 50% from a mechanic that could do you an annual, before you fly it away. That being said, I hope someone here is available to check a plane out for you, you find a plane that has just been annualed, and you find the plane of your dreams!
Best of luck.