This suggestion is probably only marginally helpful but--if you book a round trip ticket for a large enough window to fit all your visits in, you can then book much less expensive domestic flights between schools in that window. You might even be able to keep staying with grad students or something between visits? idk. For the domestic flights, airlines like Southwest have no change fees, so if you need to rearrange things after you get more news, you can. Also there are websites with student discounts on tickets, like studentuniverse.com.
Congrats on your good (though understandably frustrating in another sense) problem to be having!!