Sharpest wideangle Lens on a budget for landscapes?

[AR76]

According to Photozone
Samyang 14mm f/2.8 IF ED UMC Aspherical - Full Format Review / Test Report

Quoted from Photozone:
----The front element has a "bulb"-like shape, a fairly popular approach these days. It seems to help to control the rather tricky optical problems inherent to ultra-wide angle lenses. On the downside it's not possible anymore to mount front filters for obvious reasons. ----

Bummer! Thank you for pointing that out. Well, I guess I can still use the filters on the Canon 24-105. The Samyang 14 however is then limited to stiched landscape images, where filters are a no-no to begin with. The price / resolution ratio is too good to ignore. While the Tamron 14mm f/2.8 lens looks good, the only price quote I could find is a whopping €1030 for a used one. (You sold it for $350 ?!) I have not seen any for sale on the net so far though.