If i was you, i would go to Upfield farm (just to the east of cardiff)
£10 to land
£10 to park for a weekend
£20 to borrow a car for the weekend
I fly in to there to go and watch the Rugby. Cardiff will cost an arm and leg and it is a pain in the **** witht the VFR corridors. The strip is concrete 600x10m rwy direction 05/23. There is some towers a few miles to the east that are a great visual reference. It is also outside of cardiffs airspace.
You can get a PA28 or C172 in there no problems. I can get a Cessna 337 in there fully loaded, mind you in a fully loaded 337 you need pretty much all 600m to get out!!
PM me if you want more details.
Gary