Ready built ones are rather pricey (>$2K USD). IMO the Folger Tech FT5 R2 kit looks pretty good. I've not bought one, yet. The Tronxy X5S kit has a lot of folks working on it lately too, but after reading the blogs I get the impression those who have the X5S are busily replacing it piece, by piece, by piece... That can be a lot of fun, but not my preference.