Don't fert about - for macro you want a ring flash. Here's a second-hand Sigma for just slightly over your budget.
Waste of time - hard to diffuse and very harsh light
Yes, no real macro shooter ever uses or recommends a ring flash!
Having admired Pauls (dogfish magnet) Flickr macro shots for some time, I'd certainly accept his advice on a flash for macro work, but Paul, is a ring flash really that bad for bugs and stuff? Or is it just more difficult to get right as a beginner?
Tara