Summertime and the shopping is easy, at least for Keira Knightley. The actress has been taking advantage of some sunshine (rare this summer in London) to show off some cute — and cheap — dresses she picked up at Topshop. She wore a $70 black cotton sundress to stroll in the park with boyfriend Rupert Friend, and slipped into a $64 green pinafore dress twice in the past two weeks — clearly doing her part to bring down the price-per-wear quickly. Of course, her $930 Chanel gold metallic python “Antigone” sandals, worn with her green dress, does bring the price of the whole outfit straight back up. . .