You can get full size garmet bags for around $50. However, if you want to use it for carry-on, which you probably do if going to interviews, you will want a tri-fold bag. The Travelpro Crew4 is the cheapest one I found at $142. It's expensive, but it will last forever. And, you dont have to worry about the airline loosing it!
It depends on the airline. Some will let you fold it in half to show that it can be made small enough, some won't. It is a crap shoot just like anything else in the travel industry. The only way to be sure is to make sure the dimensions fit within their guidelines, which you can find on their web sites.
S & K had one for $9.99. I use if for overnight. It can fit 3 hang up outfits and has 4 outside pockets. Plus it can be in the overhead compartment of planes.