I do not buy the rope comfy perches for my birds. Why? Because if you buy a rope dog toy that can be untied, you can use that as a perch. And if your cages are smaller, you might get 2 out of one toy. I buy mine at the Dollar Tree so I only pay $1 for it when the comfy rope perches, which are the same thing basically, can cost up to $10 or so! All three of my cages have them now and all my birds love them! And, because they are made to be gnawed on my dogs, I think they last longer (though I never had a comfy perch so I don't really know how long those lasts).
Just knot each end about how long you think you will need in the center, and run any excess back through a few bars down or over to make it taught. The bonus: They love the ends to play with!
Just make sure the dog toy doesn't have any chemical smell or anything like that. My tiel has had his for about a year now. I noticed when my parakeet would get in the tiel's cage that he went right for it so I gave him one too, and now I put one in my finches new cage and they love it too!
Here is a picture:











