About the cheapest good macro filters/diopters/lens attachments are the Raynox brand - a DCR 250 would be a good starting point if you don't want to spend a lot on macro gear at the start.
Extension tubes (kenko brand are the best) are another option, though I prefer the DCR 250 myself simply as it clips on and off the lens - quickly letting you get back your infinity focus, whilst tubes take a little longer to remove