A failed cable does not mean you need new earphones. Before deciding whether a budget IEM is worth repairing, find the failed part and check the warranty.
The small parts are worth checking first
Worn tips, a faulty detachable cable or a manufacturer-replaceable filter may be straightforward to replace. Confirm the diagnosis and compatibility before ordering. Buying several guessed parts can cost more than getting a proper assessment.
Use the cable fault checklist for intermittent sound, or the quiet-channel guide for an imbalance.
A socket or driver fault needs a quote
Opening a glued shell can damage it. Replacing a driver also involves sealing, wiring and acoustic matching; a unit that physically fits is not necessarily a correct replacement.
Ask whether the repair includes checking both channels. A replacement earpiece from a different revision may not match the one you keep.
Compare the complete cost
Include diagnosis, parts, labour, shipping and the repair warranty. Compare that total with a replacement pair you would actually want—not just the cheapest pair available.
Repair is attractive when the fault is clear, parts are available and you like the fit and sound. Replacement becomes more reasonable when several parts are failing, corrosion is extensive or the repair has no dependable outcome.
There is no honest universal “repair costs 30%” rule. The decision depends on the fault, the quote and how much the existing earphone is worth to you.