There are two versions:

One was and still is a printed coupon that you exchange for a Octapus size card to enter or exit depending on the station. Full retail at travel agencies is around $80 for HK Central. You can get them cheaper if you have frequent dealings with the agency.

Agency chains buy these annually in bulk. Maybe HongTai is clearing out their 2015 commitment?

The other is a voucher that you print and exchange for the same enter/exit card and it was always redeem these cards all at the same time. I have no experience whether these one time use cards can be used at a later date.

Maybe ChrisLi can comment?