Our grandson LOVES to climb on everything! Commercial climbing walls were pricey (about $80 on the low side) given that we didn't know if he would like it or not, how long he would enjoy it, or how stable those plastic walls were. Here is our cheap solution - it can be yours too!
Time: 2 HoursCost: $45Difficulty: Easy
Start our with some very cheap Oriented Strand Board (OSB) sheathing used for subflooring and one of those blue tarps - we found one on the side of the road during big trash day so ours was free - if you find one that is partially ripped, that's okay, you won't need all of it. Our wood was used in a Wizard of Oz display for Halloween. Staple the tarp tightly around the back side of the boards. Then trim the tarp.
Our Son-in-law helping my husband. When you buy a bag of foot holds, you get long screws with washers and nuts for each one. Mark our your pattern based on child size, drill holes then place foot holds putting screw through wall - secure with washer and nut. Notice the "V" at the top of the climbing wall: That is the size of the pecan tree trunk we are stablizing the wall with - you'll see!
Three Simple 2x4s cut to give the grade you want on the climbing wall with cross-bars set at different levels - you can't see the one closest to the camera. See how the middle one is set flat and the side ones are set the other way? Depending on your child's wants, you can make this wall steep grade or low grade. And it can be changed as the child grows.
See how it fits against the tree? - there's a picnic table under it now, protected from the weather and brought out for lunches and snacks.