Shadegate, The actual buildings/walls etc cost absolutely nothing to make. I just hoarded boxes and bits for a while (to my wife's dismay :0)). I was also lucky that I had some balsa wood and plasticard handy. However, these weren't vital to the project and cardboard would suffice.
The only money spent on this project was for the Polyfilla and spray paints! Household water bases undercoat was used for the church and drybrushing.
Mikeland, with regards to weathering the walls on buildings just try out a few textures on card, first. Keep what works, throw out what doesn't. In hindsight, I wish I hadn't put so much coarse sand on the brown city walls, but if you do make a mistake it's always easy to correct or disguise these errors.
My biggest tip for making buildings is don't rely too heavily on dry-brushing. Thin washes are the key, they look more realistic. Heavy drybrushing is great for rough plaster or stone walls but only light stages of dry-brushing is ideal for most buildings.
Thanks for your advice, I have two scratchbuilt "peninsular" houses that are half painted and hidden so deep in a closet that they have snow on them (but it never seems to get christmas!). Now I might just have found the push to make them my next thing to finish!