I really don't think they are if you talk about table prices from the maker and similar materials. You rarely see those prices though. Most custom slippies are going to have pricier materials (stag, ivory, pearl, etc.) and often sell on the secondary market for significantly more then what the maker sells them for. That leads to the perception that they are more expensive. Of course a 5 blade slippy is going to be pricey because there are 5 blades to grind and precisely fit into one handle.