he offered to sell me his truck cheap

不好意思白天在班上忙工作,看得不仔细,可能回答得不准确。现在好好来答一下：)如果你要从语法的角度来讲,正确,这里cheap是truck的宾语补足语（cheap形容词做truck的宾补）to sell me his truck cheap相当于to sell his cheap truck to me或者你可以理解为to sell me his truck at a cheap price,但at a cheap price修饰的是sell了,所以从语法的角度还是理解为前者合适一些。类似的还有：I find it very difficult。（very difficult做it的宾补）I'm going to paint it pink。（pink做it的宾补）I want to sell it cheap。（cheap做it的宾补）I find learning English difficult。(difficult做learning English的宾补）I saw the kite up and down。（up and down是副词做宾补）前面几个都是形容词作宾补具体的你也可以参考一下有关宾语补足语的更详细内容（从语法角度来讲的）：其实我也想说,你也可以不用探究语法的,因为英语是外国人讲的,而语法是我们通过二次翻译而总结出来的。所以你如果见多这样的句子就会不觉得奇怪了,也不用去花时间探究语法了。毕竟在国外交流更多的是明白对方的意思就可以了,哪怕有点语法的错误,毕竟语言是用来交流与应用的,我们也不该为了考试而学语法。多读、多听、多说、多用英语的思维思考,不用学语法你的英语也会很棒的,而且会更纯正。祝你更上一层楼!