都可以.含义一样.不过这是两个介词的不同用法的交叉巧合.了解下列它们的根本用法就好了：
at
(indicating a rate,price,speed,etc 指比率,价格,速度等):House prices are rising at a higher rate than inflation.房价比通货膨胀上涨的比率高.
* I bought this coat at half-price/at 50% discount.我用半价[5折]买的这件外衣.
* driving at 70 mph 以每小时70英里的速度驾驶.
*old books selling at 10 cents each ...
for
= as the price,reward or penalty of sth 作为对某事物的代价、 报酬或惩罚:I bought a book for ￡3.我花3英镑买了一本书.
* She gave me their old TV for nothing.她把他们的旧电视机送给我了.
* He got a medal for bravery.他因勇敢而获得一枚奖章.
* You can go to prison for dangerous driving.鲁莽驾驶可导致入狱.