These look like Pentax mount lenses, am I right?
The 28mm is a fairly good lens, and yours looks like the metal-bodied version. The 50mm isn't a standout amongst some of the other manual 50s you can find. You'll probably get around £20-£30 for each on eBay if the optics are clean.
Not sure about the zoom, but given it's a slow aperture I wouldn't expect it to be hugely sought after... might be wrong though!