There's a lot more to making crisps commercially than just the price of potatoes.
I make root chips myself cos I dont really eat spuds but the process is the same. I use the slicing blade on my food processor stick the root veg in, you can just slice thinly or use a peeler to get them super thin. Put them on a baking sheet, drizzle with oil, season with salt and cook for about 10 minutes at gas mark 6 ( sorry no idea what the conversion is). If you want them crispy make sure you dry the potatoes off before you arrange them on the baking tray.
Some people deep fry them though, and that only takes a minute.