There are lots of factors. Sculptors rates can vary depending on experience and desired quality. Then there is the moulding cost (one master mould and one production mould). Of course, you don't have a mould made for 1 figure. There's on average room for around 15 mansized 28mm figures (size and multipart can affect the numbers) on a mould, so you'll want to either have enough figures to fill a mould or share one with someone else, so as not to waste any space (and therefore money).