Cheap rain jackets fail when you need them. Arc'teryx is actually waterproof and won't disintegrate in three seasons.
Why Not Just Buy the Cheap One?
Arc'teryx's Gore-Tex membrane actually stops water penetration with a breathable structure that doesn't clog like cheap polyurethane laminates, which feel waterproof for six months then let sweat and rain through equally. The seam-sealed construction and reinforced stress points mean the jacket survives three seasons of alpine conditions; budget jackets delaminate and tear at pressure points within a year.
The Buy-Once Math
A $100 rain jacket fails you on the mountain, gets torn during a slip, and you buy a replacement—that's $300 in three years of terrible reliability. Arc'teryx costs $400-500 and handles five years of actual weather abuse, shedding water and staying intact. One jacket that works beats three cheaper jackets that disintegrate when you actually need them.