Screen + garage + a little air movement = perfection
The "optimal" temperatures of 120 to 140 you found are for large commercial growers. For them "optimal" means minimizing product while maximizing throughput. They have a lot of hops to dry and oast (dryer) space is expensive. So they boost the temp up to speed up the drying process. They have 8 to 10 hours at most.
For the homegrower, I'm assuming you got into this, at least partially, so you could have a higher quality hop. That's what we are shooting for among our product. Once you exceed 100 to 110F, the essential oils start breaking down. These are the things that impart a lot of the flavors you typically want. Above 140F, the alpha acids break down and you have less bittering.
The oast I put together will not be heated at all. Rather it just has improved airflow and air contact with the hops. We're also experimenting with using lower temperature, cooled air. True, you can hit a point where the cone is cold enough that it won't willing give up its moisture, but we may be able to get around that, too. Granted, it will take us 12 hours instead of 8 hours to dry, but we drying less than 10 acres of hops not over 300 acres.
For the moment, just think "air contact time". How can I get more air to touch my hops. That could be by blowing the air or by spreading them out in to a very layer (1 cone deep) on a screen so you get air contact on both sides. The temperature doesn't matter as much, just keep it above 70F.
Again, it will take longer than 8 hours to dry...but what's your hurry?