Reverse a Lens - Budget Macro

I have bought a reverse mount that allows me to mount a lens backwards on my Sony DSLR. When used backwards a standard lens can be used to take macro photographs. I bought mine from Ebay for £2.99 and it came with a 52mm-55mm step ring so I can mount 52mm and 55mm filter sized lenses in reverse. I'm now on the lookout for a cheap 28mm lens to use with it.