A fair few bob.
Your best bet is to look online. No idea about any of the vendors in England, haven't been there in 3 years.
I'm no expert, but I shall give it a shot.
You will need a skimmer rated for 1500 gallons, a decent sized sump, maybe a 200 gallon or something, the skimmer will have to be external at a rough guess, a lot of lights, Halides to penetrate the tanks depth, a huge amount of rock, a lot of salt, dont know what you could use for powerheads in a tank that size.
But just from that, you could easily top 10k IMO.