As a point of reference for the cost to move up, Penn State moved both of their men's and women's hockey programs up to NCAA D1 in 2012. Terry Pegula, a Penn State alum and now owner of the Buffalo Bills and Sabres, donated $102M to build new facilities, including a 6,000 seat hockey stadium.I will add hockey has some economies of scale...
Add men's hockey. Add women's hockey.
They can share a lot of the needed facilities, administration, and management.
Having both takes care of any potential Title IX issues, whereas baseball would require a women's sport of a comparable number of scholarships... not sure which... to be added.
For the record, here are the women's sports the Big 12 sponsors that ISU lacks...
Equestrian
Rowing
...and that's it.
Not that I think hockey is coming or anything. But if you were going to add one, I think it makes more sense.
It is worth noting that before Penn State moved up, the Big 10 was not a hockey conference. Big 10 hockey started in 2013 with Minnesota, Wisconsin, Michigan, Michigan St, Penn St., and Ohio St., later adding Notre Dame as a hockey only member.
All this to say, if ISU had one or a group of passionate donors to sponsor a new hockey complex, there is a case to be made for being the eighth member of Big 10 hockey.