The sentence that is punctuated correctly is A, "the shoes normally cost 40 dollars; however, we got them on sale". The semicolon should be used because the two sentences are closely related in terms of meaning and should not be separated with a comma. Yet, as however is an interjection, the comma following it should be retained.
The punctuation in B is used when the however clause follows the subject of the sentence. The third option is not the one because the semicolon should be placed before the interjection. Finally, D is not correct since it contains no particular punctuation at all.