I assumed all Q&B's would have the same policy on cutting, my local one does 4 cuts free and charges 25p for each extra up to 4.
Try ringing Head office and see if there's a company policy on cutting or whether its left to individual stores.
I fit plastic to fascias and soffits and would charge £400 including materials for vented cover over but hiring of tower etc to reach over conservatory would be extra.
Window companies just rip you off but people use them because they feel they are getting a better job (ho hum). The jobs...
Your local college will probably run plastering courses but the drawback is that it will be only at certain times of the year. Not too expensive though.