WTB - Samyang or equivalent fisheye

I'm after a fisheye lens and interested in the Samyang 8mm or similar. I'm not fussed by box or by wear and tear, as long as optics are clean and mechanicals OK I'm happy.

Please be aware I'm on a restricted budget, hence the nature of my request, so I'm sadly unlikely to be able to afford a mint Pentax 10-17.