Here is one very popular example of a minimal bare-bones DIY piezo buffer circuit you can build yourself, or by one pre-made from the author:
http://scotthelmke.com/Mint-box-buffer.html
Here is the $58 Schatten Mini Pre:
http://www.amazon.com/gp/product/B006AVA3TQ
Here is the $99 LR Baggs Gigpro:
http://www.amazon.com/gp/product/B001E95KEW
Here is the $29 Behringer ADI-21:
http://www.amazon.com/gp/product/B000KITQK2
And there are others, that cost more, as I mentioned in a previous post.
http://scotthelmke.com/Mint-box-buffer.html
Here is the $58 Schatten Mini Pre:
http://www.amazon.com/gp/product/B006AVA3TQ
Here is the $99 LR Baggs Gigpro:
http://www.amazon.com/gp/product/B001E95KEW
Here is the $29 Behringer ADI-21:
http://www.amazon.com/gp/product/B000KITQK2
And there are others, that cost more, as I mentioned in a previous post.