Well, this one isn't quite that big (see last photo for one that is) but the design can easily be scaled up with larger materials to a prop that is very large.
This design is based on a spider we made a couple years ago, with modifications to minimize the number of pipe fittings, and flexibility to add your own body shapes and sizes. We used 1/2 inch PVC pipe because we had lots of off-cuts left over from a gardening project - I would probably choose 3/4 inch if starting from scratch.
Given the number of joints in the legs you can also pose the spider in different ways (like front legs off the ground ready to grab a passing child) or omit the last segment of each leg so the spider sits flat on the ground. We found this configuration better for use suspended in a web.
Step 1: Materials and Tools
60 feet x PVC pipe [$12.00]
1 x PVC "T" fitting [$0.40]
3 x PVC 4-way "Cross" fittings [$3.00]
16 x PVC 90 degree "Elbow" fittings [$4.00]
16 x PVC 45-degree "Elbow" fittings [$13.00]
8 x pins to hold legs to body (16d nails work fine)
2-3 x cans spray foam insulation [$15.00]
2 x cans black spray paint [?]
PVC pipe primer and glue [$9.00]
Duct tape [?]
PVC pipe cutter
Drill with 3/16 inch bit