Welcome! Sounds like you got a bargain deal now - the price of UK firebricks nearly put me off. Good find with your 250! You can build an oven for surprisingly cheaply if you're prepared to go slow and see what turns up on ebay, freecycle, classified ads and so on. You've come to the right place for advice!
I saw the same TV programme - think this is Jamie's oven here:
Jamie's oven
Carl