Hi Neil,
Thank you for your question.
Usually in the UK no-one seems too concerned about the price as the dollar/pound exchange is so much in your favour!
However, count on around 60 pounds for a case, 40 pounds each for the two transformers, and maybe 30 pounds for binding posts and other ancillaries like a mains switch, rubber feet, and a bit of good wire for internal wiring.
This would mean 325 pounds for the kit, 25 pounds for postage, total of around 520 pounds all up.
I can promise you it competes sonically with amps with retail prices of 2000 pounds and higher.
I hope this allays your fears!
Cheers,
Hugh