I'd imagine they weren't cheap back then. Mozzarella cheese was not easy to get in Surin (likely bought and delivered from Bangkok at a premium in those days) and was expensive to do so. As well as Pepperoni and Italian Salami. Nearly impossible to buy in Surin, even the first few years BigC and Makro were open. These days you can get Mozzarella easily in Surin (Makro is well stocked). But though Pepperoni and Salami are readily available they are far from being inexpensive, rather the opposite. (By the by, Makro in Buriran is always less expensive for salami and pepperoni for some reason.)
I remember that his restaurant business was not booming so he resorted to making "mini pizzas" which he took down to the Night Plaza around 18:00 to sell at ฿25.00 each. That didn't go down well either.