Great to see this finished at last.
Regarding the cost to machine this, don't be concerned by the brass piece. The material cost of the brass was £22+VAT, so a lot more than aluminium. However, brass is probably the easiest metal there is to machine and the brass part is a simple '2.5D' part, with nice vertical sides so it doesn't cost much overall. If Photekq wanted another brass piece machining it would only cost about £40-£50 including material. Still got to add on polishing, but that shouldn't be too much...
The main difficulty with machining this case is the angled surfaces, since it either requires a 4 axis machine, or carefully aligning and clamping the part an additional time. I then put the top plate and base together to machine the angle on the front edge of the top plate, so it matches the base perfectly. I do have a 4th axis for my machine, just not used it much. It's tempting to have a go...when I have time.
If the design was changed to just have normal perpendicular sides, that would knock a huge amount off the cost to machine it, but I guess it would adversely affect its aesthetic qualities.