Reddit mentions of Tw Evans Cordage 23-210 Twisted Multi-Purpose Rope, 1/4 in Dia x 100' L, 900 Lb

Yep, why not? You can also construct a lot of your own bridges and climbing poles using pet friendly sisal rope. I use it throughout my whole enclosure. I make braids out of them and wrap everything and hang them on the wall. My babies love to climb them.

https://www.amazon.com/T-W-Evans-Cordage-23-210-100-Feet/dp/B000W9QHGA

My budgies' favorite toy is actually a "tree" http://imgur.com/a/ad2Bt - this is a tree and stand that I built. Eventually I went on to paint it and add caster wheels. The branch is nearly 6 feet tall, so they get some good vantage points of the room at the top. You don't have to add much at all to the tree/branch stand, it is already enjoyable for them to play with the little wispy branches while they hang sideways or upside-down.

1. Find a source for a good sized branch
   
   
2. make sure it is bird safe (http://www.mdvaden.com/bird_page.shtml) and properly clean/prepare branch (instructions in link).
   
   
3. build a shallow bin or open box and mount branch to a reinforced plate, mount plate and branch to stand base box.
   
   
4. watch your birds explore the branch.
   
   The above option works great for small branches: install a hanger bolt into a branch and fasten it to the side of the cage with large stainless fender washers and thumb screw.
   
   Sisal rope, specifically oil-free & untreated: http://www.amazon.com/T-W-Evans-Cordage-23-210-100-Feet/dp/B000W9QHGA/ref=sr_1_1
   
   You can hang something like a coconut half or make a climbing net (http://www.craftster.org/forum/index.php?topic=310382.0) out of it. Even a two inch section can be fun for the little guys to chew on.
   
   Speaking of coconut half, if you have been to pet smart then you have seen a coconut 'hut' with two opposing halves tied with three ropes. Coconuts can be bought for $2 -3 at the grocery store. I built one myself and I am quite pleased, my budgies are more willing to try new foods that I put in it.
   
   Poplar can be found cheaply in manageable thickness at the hardware store in the form of trim board. It can be perfect for replacing missing wood from a hanging chain toy.
   
   I just recently re-purposed a swing on chain toy with coffee stirrers, zip ties, and bamboo skewers. I cut 15 stirrers in half and zip tied them together so they spread out in a ball pattern which was then attached at the end of a chain.
   
   Balsa wood can make great cannon fodder against small beaks. If you cross cut "chips" it might have the same effect as yucca chips, but at a fraction of the cost.
   
   Poplar Dowels: Most dowels at the hardware store are poplar, but always safe to check.