Don't forget about extension tubes or closeup filters. This can be an inexpensive way to get either closer focus (extension tubes) or close focus + additional magnification (closeup filter) for a lot less money than a dedicated macro lens using your existing lenses. Tubes are by far the cheapest way to get closer focus (smaller MFD - Minimum Focus Distance) but the cheap ones make your lenses preform as if they are completely manual. Some tubes do support the lens electronics so that's also something to look for but it will cost more.
I started with an old Vivitar 2x macro focusing tele converter behind an old fast 50 and got pretty nice results (IMO). That setup was good enough for a couple of years until I bought a dedicated 100mm macro.

Here's one with that Vivitar 2X TC and my A 50mm f/1.7. In fact I think this is the first photo I took with that combo.

IMGP2461 by MattB.net, on Flickr