Librands advertise their manifold complete with ceramic cat for £1360 plus vat and delivery. I had a remap done at Williams about 5 years ago and it was £400 then, so looks as if it approaches £2k overall and even more if you don’t fit manifold yourself. That’s quite a lot of petrol!! Hope this is of some help.
I had mine done at Williams in May - the cost was very similar to what you have said - £1350 for manifold and cat, and £332 for the ECU remap. I also paid £485 for the sports exhaust. The labour was £545, and then the VAT was £482! Total inc VAT was £2892.
