Individual passes cost $16 plus gratuity ($18 total) for a single person, one day pass. No scrubs. These are purchased ahead of time.
*IF* the spa allows, sometimes they will sell single person day passes on board, and the cost is $27 with gratuity, which includes scrubs.
If you want to buy the scrub on its own, it's $9....
Length of cruise pass: On the 7 night Fantasy we did, length of cruise pass was $149 plus gratuity for a single person, $199 plus gratuity for two people or a couple. These include the scrubs. For the couples pass, it's still cheaper than buying 14 one-day passes. For the single person, it's not as good of a deal unless you use all 7 days, but, again, the scrubs are included.
On our 13 night EBTA, the single pass was $229, the couples pass was $340. Again plus gratuity on top.