Good and cheap would be shoptemp.com, they ship out of china so it's not fast.
Good and fast would be some non-china-located store, for mayfly I'd recommend modchipcentral.com as they're located in canada and can get the cart to your door in a matter of days if you order fast shipping. As far as I know all UK retailers were forced to stop selling carts so I don't know of any for you.
yh i hear shoptemp also closed and that wii-chip site has a .co.uk address so do u know if they still work cause u can order but they might not ship...
also i think mayfly asked for uk as well...dunno about his flag...
EDIT: Also wii-chip is quite expensive... i mean i've seen AK2i for about $15 (about £12) including postage so £19.95 is quite a lot...
really *rushes to open a new tab to check*
yes you're right
*looks in more detail*
is it worth paying for the premium flashing service? surely that's to do with the sd not the flashcard?
If you're on a DSi/XL firmware 1.4 or 1.4.1, then the card will not run until it's updated and you can't update it until you run it, so you'd need to borrow somebody else's DS/Lite (or DSi/Xl with an old firmware version) to even use it.