I've seen a VLTOR standard collapsible for like $120    so is it possible to find compatible (not necesarily same brand) parts to put in the thing somewhere?

Vltor standard and clubfoot modstock stocks only, not including the hardware are $95 shipped from JTAC Supply.

If you already have a buffer tube (also known as receiver extension) like Colt, LMT, Stag Arms/ CMT and Vltor, the Vltor stock are compatible with the noted Mil-Spec brands.

You could buy those buffer tubes (6 position) either new or used and just shop for the lower price.

You'll also need a receiver lock-plate, M4 lock nut (Mil-Spec brands) and CAR stock wrench.

Any CAR spring and H CAR buffer would compete your stock assembly.