be interested on后加什么？

　　Just out of interest, how much did it cost?

　　我只是好奇问问，这个花了你多少钱？

　　By that time I had lost interest in the idea.

　　那时我已经对此想法失去兴趣了。

　　Could I interest you in this model, Sir?

　　先生，请你瞧瞧这个型号好吗？