I work not just for the money.

I don't work just for money.

两个句子都正确。第二句，not 否定介词短语。属于否定转移中的句子成分转移。

表面否定谓语动词，实则否定状语：

1.  They didn’t come by train. 他们不是坐火车来的。

（not 否定介词短语 by train，相当于 They came not by train.）

2.  You can’t fool people all the time. 你不可能一直都在欺骗人。

3.  We can’t judge a person by his appearance. 我们不能以貌取人。

4.  They never talk about that matter in public. 他们从不在大众场合谈论那件事情。

5.  Don’t read in the sun. 不要在阳光下看书。

6.  Don’t talk with your mouth full of food. 不要口里含着食物说话。

7.  The ant is not gathering food for itself alone. 蚂蚁不只是为自己采食。

8.  She had not been married for many weeks when he saw her. 他看见她时，她结婚还没几个月。（不是“没结婚”）