Mavic Open Elite is the obvious option at £20. Halo Aerorages are available for a few more quids.

Anything else? Can’t find much on special.

Anything that wins out over the two aforementioned options will have to be under 500g and under £25 or so, and 32 hole because I’ve got hubs waiting. But those are the only main criteria. Width isn’t important, they’ll only be carrying 25mm tyres. Black or silver (or, er, purple ano).

Exal lx17 meet your price criterion but not the weight one. They’ll last longer than the Mavic’s though, thicker braking surfaces.