Please PM the price as well,
what machines did you finally end up getting?
On shirts how do you work the designs onto a black shirt since dye submission is best on white/light
I would actually use white poly embroidery thread and sublimate that on the darker substrates. Gives it an embroidered look, but you don't have to do the complicated digitizing if it was all embroidery. Plus you are able to use cotton and blends instead of just pure poly due to the fact that you are only sublimating on the pure poly embroidery thread.
Other then that, you would have to sublimate the white shirt black around the design. If you use this method, I would suggest using a shirt that you have to sew up afterward. Otherwise, the armpits will be an issue with getting sublimated at the very least.
I don't know of a black poly shirt that would have a white space for a sublimated design (at least the white space positioned logically for this application) like you have on black coffee mugs with the white band around them to sublimate.