Buy from a junkyard, or buy from me... I can sell you a full set for $300 plus shipping, and that would include brand new pads, freshly resurfaced rotors with plenty of material left on them, uncut emergency brake cables, brake lines, along with a brand new uninstalled pair of Energy Suspension trailing arm bushings.
What you need for the easiest install:
Trailing arms from 90-91 CRX Si
E-brake cables from 90-91 CRX Si
Brake lines from 90-91 CRX Si
Unbolt the old trailing arms from the car, run the new brake cables, hook up the lines and bleed the brakes. There's more to it than that, but the rest of it's not hard to figure out.
Other compatible trailing arms- 99-00 Civic Si, 92-95 Civic with rear discs, del Sol with rear discs, Integra with rear discs... you just need to have e-brake cables from the 90-91 CRX Si.