I got this for $175. It works great!
The best is neither bottom nor top but the side. The fan and element are situated usually at the back and they blow warm air across each rack in a much more uniform fashion. The best manufacturer is Excalibur, or a knockoff like this LEM.
If you have the choice find a unit with the fan/heating element at the rear instead of the top or bottom. Also square is easier to work with than round. I have the 5 tray version of this http://www.amazon.com/LEM-Products-Dehydrator-Digital-Timer/dp/B004VLKT3W/ref=sr_1_1?ie=UTF8&qid=1451493203&sr=8-1&keywords=dehydrator+lem Which is the LEM version of this http://www.amazon.com/Excalibur-3500B-Deluxe-Dehydrator-Black/dp/B002SHNIW0/ref=sr_1_2?ie=UTF8&qid=1451493100&sr=8-2&keywords=dehydrator+5+tray.