Even if I was loaded, I'd still get a fixed screen over pull down one and look at ways of disguising it when not in use if it's not in a dedicated home theater room, you avoid a load of issues and £ for £ you get better quality screen (even a giant Black Diamond screen costs less than some motorised ones!).
As I've said in several threads, you can DIY a high quality screen quite easily for a fraction of the cost of buying one from a manufacturer;
Sheet of thin MDF (up to a certain size!), prime one side, paint, border with black velvet tape. Specific paint depends on room conditions really. I don't have great ones so I'd be using AVForums Black Widow mix, which is a grey screen with aluminium flecks in, meaning you gain some of the contrast you lose from having grey over white, but keep the advantages of grey (less glare, better blacks) in non-optimal rooms.
Going bigger, you could make a frame and stretch a canvas (no slack!), then paint that. Border with black velvet tape.
Or if possible, you can just paint the wall and border it.
Hiding it... I've seen several techniques (again, depending on screen size):
Theater style curtains
Pull down blind (use own fabric)
Roman blind (as above)
Wall-hanging
Or, if your son is indifferent, just leave it 'out'.