。
Buying quality is economical.
Literal
Good-quality [of-の] goods [object-を] buying [subject-は] economical [copula-である].
~のは + [adjective]+である is the cleft construction for evaluating an action — foregrounds the nominalized action with の and pronounces an adjectival judgment on it. 経済的 ('economical') is a な-adjective functioning predicatively with である. A financial-maxim statement.