I won't show you any photos of the cage since it's overdue for a cleaning, lol. Here are some pics of a hanging gym I made. It was really really easy and cheap to make. If you have a hook in your ceiling already you don't even need any nails, screws or drills. Hanging gyms are probably easier to make than standing play gyms because gravity does all the work of keeping the perches in the right places.
If you're interested, this is how I made it. (imperial measurements are wildly approximate and if you don't understand metric, use your judgement!)
Ingredients:
-Eucalyptus branches (or any bird-safe wood) $0
-Pruning saw $3
-Sandpaper $1
-Spool of cotton string $2 (+ scissors)
-10 metres (30 feet) of sisal rope $25 (i could only find a thin rope though, if you can get a thicker one it's better but will cost more)
total = $31!
1. cut the branches with the pruning saw into six pieces about 3 - 6cm (1 to 2 inches) in diameter and about 50 - 80cm (2 - 3ft) in length.
2. Sandpaper any rough spiky bits left over from the sawing and any nodules left from thin branches that may be spiky/poky.
3. Cut about 3 metres (9 feet) of the rope, and double it over. Tie a loose knot at the doubled-over end, so there's a loop of rope.
4. Cut another 3-metre (9 feet) length and thread it through the knot, start at the bottom of one side, go over-under-over-under the bits of the knot through the loop. You should have a loop, a knot, and four lengths of rope hanging from it. Tighten the knot if you can.
5. (See step 9. before continuing) Lay one branch on top of the other to make a cross. Fasten them together using the cotton string (look at one of the pics above).
6. About 40cm (1 1/2 feet) down from the knot, fasten the cross to the rope with string. (Make sure the lengths of rope above the cross are all the same length so it's not tilted at an angle) Hold it up so you can see which bits of rope are next to each other.
7. Fasten one branch to the rope at the end using two bits of rope that are next to each other. Fasten another branch with the other two bits of rope.
8. Fasten a branch 10-20cm (4 - 8 inches) above the ends of the two branches, then the same on the other side (You are trying to make a sort of square shape at the bottom).
9. Make a rope ladder by doubling over the remainder of your rope. Make a twist at the top so you have a circle about 40 cm (1 1/2 feet) in diameter. Fasten the twist with cotton string, and fasten together the rope a handspan on either side of the twist. Keep doing this all the way down and you'll have a rope ladder. (look at the pics for what it is supposed to look like) Hook this over the two branches that will be your cross before fastening them together. This rope ladder will hang down the middle of your play gym.
Oh and with the nets, don't buy them, make them! I have seen some absolutely unbelievable prices for made up nets, totally not worth it. There is a special knot you do, and once you get the hang of it, it's quite easy. I don't remember what the website was I saw the instructions for the knot though.