actually,sometimes it does not really mean 1 credit hour = 1 lecture per week because i do have lectures which are held twice a week but are of 3 credit hours and in addition, the fee fully depends on number of credits you are taking like 6 credit hour class will be costlier than that of 3 credit and usually some classes do includes the labs but the labs are of 0 credit hours coupled with 3 credit hour lecture so it means you must have to take a lab as a co-program with the lecture (where its applicable) but the labs will not have any impact on your pocket at all ;means to say they will be free of charge.and yes , the 3 credits hour class takes 1 full semester to finish off but mostly,6 credit hour class requires 2 semester to get complete and will have more weight-age than that of 3 credit while counting all of them up for the graduation completion ,for an example ,different degrees requires different amount of specific credit hours to end up with a graduation like if you a taking a BSN degree that requires you to complete 120 credits to graduate from nursing school ,you can either take 40 3 credits hours specified classes or 20 6 credit hour classes to finish up the degree but yes do remember while taking 6 credit class,as it has a higher weight age,thus,will also has a greater influence on your average GPA than what 3 credit hour class actually has.So,there are some advantages of taking the 6 credit hour class but balances out with its drawbacks if you dont do well in it.
Hope it cleared out your querry!