In case you can't find them (I couldn't for ages), they are under the JJD Buildings section.
Website says they are a fiver each. I don't remember the unpainted price being as high as that when I bought them. Oh well. Perhaps I was so keen to get them in time I didn't care about the price. That sounds like me.
I guess if you want lots and are on a tight budget then they might not be for you (I didn't realise that, sorry). Not sure what to say on the whole scratch-building idea, I'm pretty rubbish at that kind of thing. The only thing I've ever scratch-built was the giant Kong gate. At least that turned out well, though.