But to give you an idea, I bought my 17mm probably 8 years ago for $200. That was the used price and it's some off brand rather than a company you would have heard of (e.g. it's not a Canon/Nikon/whatever).

I thought it was neat, though, that someone got creative -- they made a lens adapter to add regular camera lenses to the digital Casio (see their demo and how-to at above link).

The parts for the adapter are cheap ... except the lenses themselves. How much do those tend to cost?