$1k for an image slider strikes me as completely reasonable. As csomar relates, lots of work goes into something as "simple" as an image slider. That's why (as I mention in a separate comment) non-tech folks will always struggle with the cost of development. If it were easy/fast/cheap, they would do it themselves.
$1k also sounds cheap for an image slider, assuming that it was made from scratch, tailored for the client's specific purposes and had all the related issues (cross browser, graceful fallback, etc etc) taken care of.
If the task could've been solved by configuring any of the 9000 free image sliders out there (I've opened sourced a dojo-powered one too), then $1k is really expensive.
