There's
this which is brand new but none of the 100 - 300mm f/4 at a reasonable price Jessops are selling it for £599 according to camerapricebusters, that's a good price for a lens which is quite highly regarded.
The DO lenses are very expensive for a lens which covers the same zoom & aperture range of a much less expensive conventional one. The plus is the reduction in size & weight but it's not much in this type of lens, but the downside reported by many people is a loss of contrast which to most is unacceptable in all but the brightest of light. check out Fredmiranda to see what other users think, & photozone for objective tests.