Sometimes you can buy a case of bananas for a steep discount- a friend of mine has an arrangement with one of the local grocery stores. She calls them once a week or so, and if they have too many bananas, they sell her the 40-lb. case for $8. That's $ .20/lb. This week I found some at NPS for $4/case!
To dehydrate them, you can, of course, use any dehydrator available, or even dry them on clean window screens on a hot roof or in a hot car...
Mine, so that you can get a size comparison, is an American Harvest (now Nesco) 'GardenMaster'. (I got it used through the local Classified ads, 15 years ago, for $40.) I have the extra trays, for a total of 8. Each tray can hold almost 2 lbs. of sliced bananas, 15 lbs. total. So the 40-lb box fills the trays twice, with enough left over for a double batch of banana bread (to freeze) and eating a bunch fresh.
I dry them on about medium heat- 120 degrees F or so, and it takes about 18-20 hours. They'll be a little bit more dry if you let them cool before packing into jars.
If you want the dried product to be a little lighter in color, you can coat or dip them in a lemon-honey mixture. Combine 1/4 c. honey, 1/4 c. water, and 2 Tbsp. lemon juice. Mix well. The easiest way to use it is put it in a clean spray bottle and mist the slices once they're on the tray. The photos below are of untreated slices.