That is correct, Larry. At that time of day on a weekday it will be full-whack on the price, I'm afraid.
Although changing trains at Clapham Junction is much easier than it used to be, it is still no walk in the park. You will learn how a salmon swimming upstream in a fast flowing river feels. There are plenty of displays indicating what platform you will need. Trains to Gatwick, Three Bridges or Brighton, among others, are likely to stop at Gatwick, but it would be worth your while planning exact trains online and having a plan B and C incase there is any hitch with plan A.
Southern and Gatwick Express are both run by the same company who also run Thameslink. Southern is currently in industrial dispute with its drivers (you might call engineers) and guards (you might call conductors) so a number of trains have been cut from the timetable and there are sometimes delays.
If you are travelling soon that may affect you, so you really must have a B and C. If you are travelling somewhat later things may improve but many peoples' jobs are at risk, as is safety, and both sides are well and truly dug in for a protracted fight so there may be fallout for some time.