try ebay for used macro lenses, just watch for lens that say there are macro (sigma) but they are 1:2, you should look for 1:1 ratio
a longer focal length is ideal e.g 100mm, as you dont want to up on top of your subject, but you can get shorter lengths if the longer ones are to expensive e.g 50mm or 60mm
You might try a close-up filter, perhaps to give you an inexpensive taste for macro. Also, people often buy reversing rings to reverse mount their a lens on their camera, allowing them to focus quite closely.