Dunno if you can get a decent pair for £30. But you can for about £8.
I find I'm using my photochromic lens Bolle Safety glasses from eBlag far more than me super top end interchangable lens extreme rodie race bladed team laser TDF killer specs.
The bolles are great to wear, especially if you are doing evening rides from bright light to heavy tree shade etc. Plain dark lenses are a pain in the ass then.