Deltaprinter promises low cost and high quality of prints and plan to go on Kickstarter soon. They use spectra fishing line movement system which delivers higher precision then belt drive. It will be under 500 $ and open source.
Update video from the Maker Faire 2013
Source:
https://twitter.com/Deltaprintr
http://www.deltaprintr.com/
http://www.youtube.com/channel/UCCGiCEfWBzHlndUXny0owVA?feature=watch
Update:
Deltaprintr is now on Kickstarter
http://diy3dprinting.blogspot.com/2013/12/detaprintr-is-now-on-kickstarter.html