Do you have a good shop/construction teacher at your school? Absolutely amazing resource for props in my experience! If you have a theater teacher that's good with scenery they're your other best friend!

All that being said, I would try and make it yourself at that point. You could use wood for the structure of that temple and then use the foam insulation boards for the outsides.You can carve into those then and paint that surface. There's a really cool Theater Scenery/Set Design group I somehow ended up in on Facebook that I've been stealing ideas from. You could also do it in printed fabric and build the frame out of PVC.

Trees you could use PVC potentially too and wrap them with insulation or foam to build it out.

No matter what, think about how you pull things apart for transport, getting them into a building for storage, etc. Props can be a assive pain!

Good luck!