This article might provide some insight:
http://www.kenrockwell.com/tech/best-macro-lenses.htm
Here’s another approach that I took…get a proper macro lens, but an older manual focus version, just to see if you really need one. I bought an old Sigma 60mm macro off ebay that could focus down to about 5cm from the front objective. I would just leave it at the minimum focus distance, and move back or forth until the image was in focus. I got some amazing results. I did that for about a year and then sold it for the same amount again on eBay.
I then bought another Sigma, this time a 28mm f1.8 EX DG which has quite a good macro focus option. This is my only lens, and does OK as an alrounder (with a DX body) but the macro comes in real handy for flowers/insects etc..
To be honest, I wouldn’t be too sure what to buy as a dedicated macro lens as I don’t think there has ever been a good range of prices for decent items to choose from. I remember nearly splashing out on a Nikon 105mm f/2.8 G VR and that’s probably still the best, so maybe try and get one of those second hand. I just checked on eBay, and those seem to sell for over £400, so might be outside your range.
So not too sure….good luck.