This is a complex question =-)
there's only one software that allows for true DSD editing, Sonoma Systems. This software however relies on sound card dependencies.
DSD cannot be edited because there's only one bit, therefore it cannot be manipulated. At the point of edit Sonoma converts the audio to multi-bit DSD, and then goes back to 1bit after the edit. This allows for manipulation at the point of the edit. (This is similar to PCMs 32bit float)
The other software that allows for editing DSD is Pyramix. It however, doesnt stick with DSD. At any edit point it converts to DXD (Incredibly high resolution PCM) then back to DSD. So, digital conversions are happening at every edit point.
Now for a cheap option, you can go for the Korg AudioGate Software. This is for playback and not editing but you can do basic fade-in/out and cutting a song up. But this wouldn't work well for multi-track recordings, but you can take 2 mono DSD files and create stereo interleaved file.
Here's a great website that has info on DSD (and some free downloads): DSD-Guide.com