What would be the best wide angle lens setup? excluding the E10-18

If you go for the 8mm Samyang/Rokinor lens, get it from someone with a reasonable return policy in case you have color problems. I didn't have problems on my NEX5n but did on the NEX7.

You could also get an adapter and find some used 10 or 12 mm lens in a different mount. Adapt it and use it manually.  Should come in under your budget. I would not worry about the manual focus. Set the camera on aperture priority, turn on the focus color peaking option and set it to a smaller aperture. You will be in focus from fairly close up to infinity.

There is an Itunes  app for determining depth of field so you can calculate how to preset the lens so you hardly have to touch it. I r

Also you can eliminate a lot of the distortion on the 8mm (which I happen to like) by leveling the camera if possible. or setting it up so you shoot  straight on not with the lens tilted up or down.  It makes a difference I understand.