。
I can't afford to buy clothes regularly.
Literal
Clothes [object-を] regularly buy余裕 (margin) [topic-は] is-not.
余裕 ('margin / room / leeway / spare capacity') is a key concept in Japanese — refers to physical, temporal, or financial spare room. 余裕がない = 'have no room / can't afford.' 定期的に ('regularly / periodically') is the adverbial form of 定期的 (~的 suffix).