I'm afraid there is no such thing as low cost and DSD mastering software.
Your recording, editing and mastering options for DSD are as follows:
Sonoma (probably the most popular but quite expensive)
Pyramix (doesn't actually edit in DSD - only in DXD)
All of the above systems are expensive and proprietary. There are some Philips Pro DSD/SACD authoring tools - these are also expensive.
Then you get to the point where you realize that you must have the converters which can handle DSD/DXD (for the Pyramix) and you add another $7K to $30K.
I'm afraid there is no cheap solution.
On the other hand, I've been doing a LOT of research and experimentation on the matter and started to come to the conclusion that not only is it more convenient and cost-effective to start at High Rez PCM and then upconvert as a final product to DSD/SACD, but it's also beneficial in some areas (especially noise figures and shaping.)