I was in my local ASDA (Wrexham) earlier and found they had the usual collection of Tatty Ted, Forever Friends and funny Valentine's cards most £1/ £2/ £2.50/ £5 each even for the large ones which you'd pay much more for in Clintons etc.
Then I spotted the ADSA smart (value) card for as little as 7p which looked kind of cute! on the front it reads:
Be Smart (in heart shape)
Be My Valentine
and inside says: My love for you is priceless
With the credit crunch this definately means theres a card whatever your budget! I saw a few students etc snapping them up. Sorry no pic, maybe someone can add one?