Shirox... which DMK21 got so many model with different resolution. I guess you referring to the one with 1600 x 1200 pixel res?I bought my QHY5 and Mini-borg (Used to own it but sold it) 2nd hand from a bro here.
But I think you can get them at acceptable prices at astromart or cloudynights.
The reason because there's a bigger pool of astronomers there as compared to singapore so, you can find alot of goodies and good deals if you know what and where to find.
all of my images were autoguided with either QHY5+mini borg 50 or DMK21+miniborg 50.
I do find using the DMK21, the stars are tigher and resolution is much better, which is important for guiding as well.
Where to get the Miniborg cheap?