Building a Climbing Wall and Cargo Net

My wife was looking at play structures to give our three kids something new to do when they were playing in our yard, and hit on the idea of a climbing structure. After looking through a variety of options available online, we found that most were either too large for our small postage-stamp yard or made entirely of plastic which were impossible to store in the winter and priced at $400 and up. Now I am not a carpenter by any stretch. I am a computer programmer by trade and was never particularly inclined towards manual labour, but I concluded that I could probably build something that was well suited to our yard and would serve our kids well.

So I set off with the following list of requirements.
1) It must have two climbing components, a rock wall and a cargo net.
2) It must be sturdy enough to hold 3 children at once.
3) It must have a small footprint.
4) It must be portable and it must be able to collapse or fold for storage during the winter.
5) Total cost of materials must be under $400 CDN and be built using commonly accessible tools (using either what I already had on hand, or could borrow from my father - only tools that I already knew how to use).

Here is the end result.

Complete Design, Assembly, and Construction Plans