I thought it might be of interest to others to tot up how much this project is costing me so far.
12mm MDF Board: £30. The board itself was only £15 but I had no choice but to have it delivered which doubled the price. I got it cut to size for free though. The slim board can be stored out of sight in my room behind the piano, which is an important consideration. Other options I considered would have been cheaper and able for me to carry home in pieces, but when assembled would not have been able to be hidden so easily.
9mm Cork Tiles for modular terrain £72.39 The price of cork has shot through the roof. I had to buy more than £60 worth to get free delivery, so my order includes 12 thinner tiles for making buildings. I still consider this good value as I will have more than for my immediate needs and once made, the terrain will last for many years.
I have also saved @ £30 on not needing to buy a river.
Running total: £102.39