Pre-Purchase For Spa, Internet and Dining?? When does it close?

[SeaNStars4Me]

I want to pre-purchase a massage, internet and dining package. They say the prices are less than they will be on board. Wondering if that's even true (sometimes they offer "specials" once you're on board) and if anybody knows when these pre-booking offers close? I'm about 3 weeks from sail away. 

[Tierun]

Massage prices specials can be better onboard while in port. The pre booking ends 2 days before embarkation