"Holy Spirit" and "Holy Ghost" are the only expressions in my opinion to refer to it. http://en.wikipedia.org/wiki/Holy_spirit
I think "Saint spirit" is a wrong litteral translation (by automatic softwares), as here: http://goo.gl/NtkoVy
"Sacred spirit" refers to another religion, probably Amerindian.
There are a couple of reasons why "the sacred spirit" is wrong, but the most important is that Spain and the Spanish-speaking world are predominantly Catholic and so this particular phrase is reserved for the Holy Spirit/Ghost of the liturgy.
As for your preferred phrase, "the sacred spirit", is most commonly translated as "el espíritu sagrado" and you will see it whenever Native American spirituality is discussed.
There is the problem that "the saint spirit" is meaningless nonsense as you say, but it is a literal translation that must have been added to stop people whining.
The Sacred Spirit - El Espiritu Sagrado.
Santo can mean Saint or Holy.
Santo Domingo = Saint Dominic - San Diego/Santiago = Saint James - San Miguel = Saint Michael
Espiritu Santo = Holy Spirit - Iglesia Santa/Santa Iglesia = Holy Church - Santa Biblia/Biblia Santa = Holy Bible