In what could amount to the ultimate DIY project you can now make your own AFM head using instructions from the LMU Munich.
The instructions are a tutorial for building a cheap and simple AFM head suitable for single molecule force spectroscopy. Most of the structure is build using rapid prototyping methods and it is then simply screwed together. As a 'home made' device it has the drawback of coming with no training or support, but can be constructed for a very small fraction of the cost of a commercially available AFM.
The instructions are available at http://www.biophysik.physik.uni-muenchen.de/PlasticAFM/