"in" or "for" ?? sometimes confusing!

sometimes i am quite confused about whether to use "in" or "for", i hope someone would help me clear my confusion.. this is very important to me... (i am an Eng tutor in fact, but non-native) thanks

for example... in this case, let's talk ONLY about grammar but not the meaning.

A. " the machine will be sold for $3000"

or B "the machine will be sold in $3000"

i am not sure if both, either or neither of these two sentences is grammatically correct..

i think A should be correct, and it means " i will pay $3000 exact to get the machine..."

and I think B is also correct , but it will mean " i will pay $3000 exact or less than $3000 to get the machine...


ok, but i am not sure if my thought is correct. i hope someone would correct..

i know " i will get it in one day ..." that mean i will get it in the very near future, not more than 24 hours..."

but i don't know if this applies to money too.

thanks!!

Only A is correct.

As this is a forum for people interested in learning English, please use capital letters for the first person pronoun and the first word of a sentence. Thank you.