A cheap way of approximating a macro flash is to take a piece of white card (or a polystyrene foam tile) and cut a hole in the middle so that your lens, with lens hood on, can poke through it. Then find a way of placing a flashgun beside your macro subject, but out of view of the lens, and far enough to the side to be shaded from shining into the lens by the lens hood, and point the flash at the lens. The flash will illuminate at least half of the ring of white around your lens, which in turn will illuminate your subject in a ring flash sort of way. If you have two flashes, one to each side, you can arrange for a perfectly round ring flash effect.