That sounds like some great news and lots of progress. Must be nice to not only know what you want, but to be able to get it so quickly (relatively speaking, of course!) I hope you do get that rental. But maybe the interviewers will even take into consideration that you are "in-between" instruments for the moment and have a top notch one coming. Do they do second rounds of auditions that would be after May 21? After all - that's what they do on American Idol.
Best of luck with the next round of both the auditions and the instrument hunting.