There was a thread recently on the comp.sys.dec newsgroup which ended up with the suggestion from David Riley that he would be prepared to build an FPGA-based board with a QBUS interface on one side and an SD interface on the other which anyone could then program to emulate any disk/ controller they like. I have been in touch with him to see how much interest he has had, because he needs a minimum number of about 10 to make it viable, but so far there has only been me and one other person showing an interest. David reckons they would come to a little over $200 each (possibly less if there is more interest). David is not yet on cctalk so he agreed to let me cross-post this to cctalk on his behalf, but I have cc'd him so you can reply direct.