Cobra (Cardiff) or the Swansea club on the Welsh side, both a little further along than Newport, but both run on sunday daytimes...check their websites for details...both are linked in various threads in the WRCA section.
Nothing running indoor/outdoor offroad in the Bristol area unfortunately...although I'd love someone tell me otherwise?!?!
WORM near Weston-super-Mare run offroad micro's on Tuesday nights every other week, but they don't run 1/10th as their hall is a little small.
Hereford is the next closest one after that I think...which isn't really that close at all, and they run Friday nights as well.
Not sure the Gloucester/chippenham area clubs run offroad at all.
It's a little weak in the South West area currently
EDIT: Hehe...Dave just beat me too it! Pity your efforts in Bristol never came to anything dude..would have been cool...but as you've said, expensive too!