I guess you'd say I don't have a budget option, because I have the Nikon 105vr. And it's the perfect combination of focal length, VR and size for walk around macro. If it's too expensive, you want something as close as possible to it, in my opinion.
You want VR, though don't expect it to do much at true macro distances. You want autofocus, probably. You want somewhere around 100mm. Shorter is too short. I have the Nikon 60mm micro, and I've almost never used it, because (on FX) it's just too short. When I try to get close enough to fill the frame with something I could do on the 105, I'm practically touching the subject. I'd say don't go any shorter than 90mm, unless perhaps the Nikon 85dx macro does something for you.
Since pretty much all macro lenses out there are plenty sharp with nice flat fields (for macro), don't get hung up looking for 'the sharpest'. They'll all be sharp enough. You might research if a lens is a lot worse at distance though, as some macro lenses are very much designed for best performance at very close range, to the detriment of distant subjects.; I find my 105vr to be good at both near and far.
Suggestions would be the Tamron 90mm, or a Tokina 100. If you were planning on doing a lot more macro than non-macro, and especially if from a tripod, you might look at the longer Sigma options that include a tripod collar.
