Hi Nigel,
The remote sensor which allows you to control the sky box is an IR cable that comes with the PU-1H7. Each PU514 balun comes with an IR cable that acts as an IR receiver.
Your costs are about correct:
PU-1H7 -> £1k-£1.5k
PU-514 -> £130
Netgear switch -> £30-£100 depending on the number of ports.
I'm afraid my knowledge of what's available and suitable is quite limited. I'd recommend you chat to a dealer and see what they recommend.