When I was at Saints we didn't really get much in the way of civvy traffic bar a twin that was hangared there. You need Crown Indemnity on your a/c for starters. Cardiff (Barry) is GA friendly and just minutes away. Sorry I can't help you with costs, I haven't been there for a few years! Unless you are military there isn't really much in the way of scope for needing to land there, it's not massively accessible by foot being a larger camp and it is in the sticks! Buses are much more frequent out of Cardiff Airport. It's a far cry from the likes of St Mawgan used to be....