If your retailer told you the card would work with your hardware/software combination it would have constituted a condition of the contract - i.e. you relied on the information when making the purchase. In such a case you would be entitled to a full refund if the card didn't work.
In your case you say you were 'told it should be OK' (which is rather vague), and you say that your machine meets the minimum requirements printed on the box. It's the last part that's important - your computer complies with the maker's minimum requirements - and on the face of it you aren't entitled to a refund. You won't need one if the retailer can get things working. Anyweb seem to be doing the right thing, and if they replace the card with a working one you haven't any grounds to complain.
You mustn't expect to profit from the interim change in card price - that's not how it works. You were happy to accept the price when you paid it, and you must live with that.