The big problem in Hawai'i is the price of real estate there has sky rocketed. Too many folks want to live there and not enough space to go around. I don't know if UH has room on campus for such a structure but as mentioned, the cost is going to be high. There is currently a building boom on Oahu which makes construction materials scarce and expensive on top of everything having to be shipped in from other places.
Was21 mentioned the flea market and right now that's about the best thing going on at the stadium. If you ever visit Oahu go to the flea market (twice a week - Sat. is the best day) and get all your touristy junk. Fellow Hawai'ian shirt lovers this is where to go.
I've been fortunate in that I've been to Oahu a dozen or so times and have been to 1 Pro Bowl, 1 college game, (Hawai'i vs BYU, Hawai'i won), countless flea markets and have seen The Rolling Stones there. Hope they are able to build a suitable replacement.