Japan has produced a whole array of really wonderful cassette singles all of which are now very hard to acquire, although this is not reflected in their price, as most cassettes can be found for under £15 ($25).
The first every Japanese cassette single was issued in 1984 for "Like A Virgin And Other Great Hits". This, as with most cassette singles issued in Japan included same tracks as the 12" (and CD). The casette sleeve was made of card and came in plastic 'album style' casing, similar to album cassettes. All Japanese cassette singles come with plenty of Japanese writing and are easily recognisable.
"Material Girl" followed in 1985 with an equally rare "Club Mixes" cassette single. "Dress You Up" also offered an early rarity, all of which would certainly fetch £15 minium in mint condition I'm sure.
1986 saw three more cassette singles, issued for "Live To Tell", "True Blue" and "La Isla Bonita", all of which have become as collectable as the very early ones. "Causing A Commotion" followed in 1987 and does seem to be the only cassette single issued in that year.
The next known cassette single was issued for "Like A Prayer" in 1989, followed by "Keep It Together". The final known cassette single was issued for "Vogue". Very few seem to appear for sale and even the latest pressings can be hard to acquire.