Based on that full API integration did cost 14k and latest updates to API are 7k, my guestimate would be somewhere in the middle say $10k depending on all the ‘nice’ features you want to have.
However I would recommend to eye for some kind of B&C integration as the next step as it would make NuDroid even more resilient, but I have to declare an interest as B&C shareholder here 
Henry suggested an integration with NuLagoon, but given it workings that might be a bit complex to make it seamless and user friendly. Maybe something for the next release? Like to hear opinions of others.
I would explore both first before looking into BlockTrades. We don’t know much about that company and who is behind it and whether they are still around next year. Just my views.