Keep an eye out for the next one T-Man. You will be welcome.
Dekker is right to bring up train tickets. They can be a total ripoff if not bought exactly right. If you have an annual travelcard for the SE region (FCC, Southern, SW trains etc), that will also net you a third off. None of us are travelling during peak time, so avoid those Anytime fares that the automated ticket machines love forcing you to buy.
If you are buying a single each way and don't have a travelcard, it's best to wait 'til I'm there to buy your ticket south. I have to have an annual ticket for work, and it lets me buy discounted tickets (a third off) for a couple of guests so long as they travel with me.
I don't know if they offer any discounts for buying in advance on the Thameslink route. I don't think so.
It looks like the cheapest way to book tickets is to buy the open return for £24 (minus any discounts you can get personally). You probably can't use my discount that way, but it works out nearly the same as a discounted single down and non-discounted back up.
Aren't trains just stupidly complicated?