Jill has covered this topic really well, above! I would add that I bought one of the cheaper round dehydrators with stackable trays and a fan at the top (Nesco brand). I find that having to stack the trays IS a bit of a pain (I've dinged a few cookies when putting the lid back on) and the racks are a bit sloped. But if my cookies are outlined, it works very well.
If I had to buy all over again, I'd probably pay a few extra dollars and get a sliding rack-one like the Excalibur.