don't use rings; get a cantilever mount -- less hassle, correct height and proper eye relief. there's a good comparison here
, but it boils down to the PEPR being the best option in the around-$100 range, as the others said.
ETA: it's supposed to be at the same height as your irons; that's the right height. the front sight will blur out as you zoom in; if that bugs you, get offset irons, a QD mount or both.