Best exercise for IPF?

I've had some lung disease for maybe 2 years now. At first the doctors didn't call it IPF it was just some crackling noises in my lungs when I breathe. Since having pneumonia earlier this year and was hit hard with it I can't get my lung function back. Since seeing a pulmonologist last March it was called IPF! After going to pulmonary rehab and basically just exercising on a NuStep machine I still have SOB. Medicare only pays for so many rehab sessions so I am wondering if walking is as effective as using a recumbent NuStep machine. I have 20 miles to drive to get to an exercise area. I'm thinking of buying one machine like that but they're quite expensive. Any thoughts about what's best?
Thanks!