1) take a 50mm lens. reverse it and hold it to your lens mount. - cost: free
2)take a cheapo sigma (macro) zoom lens, the **** sort that really doens't do macro but about 1:2.5 and attach a 2x converter on it.
- cost: if you have the stuff this should be free too. If not, a 2x converter is useful. the lens can be bought and sold 2nd hand according to project.
3)Get an extension tube - you lose infinity focus, difficult to reconcile with the rest of your setup. -cost: about $30 - 50
personally my favourite approaches are 2 followed by 1, with 3 being the last.
otherwise, just get a macro lens and be happy with the incredibly sharp images it will produce.