Old houses mended, Cost little less than new before they’re ended.

Cibber’s couplet uses a homely, practical image—repairing an old house—to express a broader truth about “patching” what is worn-out. The sense is that once a structure (or by extension a plan, institution, relationship, or reputation) has deteriorated, the effort and expense of continual repairs can approach the cost of starting afresh, especially because hidden defects keep appearing before the job is finished. The line carries a mildly satiric, worldly wisdom typical of Augustan verse: it cautions against sentimental attachment to the old merely because it is old, and it hints at the self-deception involved in believing a quick fix will be cheaper than a rebuild.