I tried to combine as many trips as possible. I carried around my calendar all October and November, checked my phone messages 5 times a day, and my e-mail 20. I wouldn't necessarily recommend doing it that way. But I was able to do 2 interviews in cleveland in one flight, and did a few road trips. Cleveland to Ann Arbor to Chicago was one.
Figure out where you know people, whether it's cheaper to fly or drive, and stuff like that. Sorry, no magic tips from me. Hopefully, someone will have some.
There is no way to make it affordable other than only interviewing wherever you live now or within a 1 day RT drive of there. Combining interviews in a single trip and couch surfing are the other things you can do.
I interviewed at 16 places in the NE, Midwest and NW and did it in 2 1/2 trips: one driving trip around New England for Dartmouth, UMass, BU and Yale (plus a day trip back to Boston for MGH), one to the midwest for 5 other places and then I headed out west straight from there. Otherwise I hit a few other places as day trips from NYC.