ok this isn't card magic, but it is under 4 quid. I would thoroughly recommend "Pena Coin". It is still one of the greatest reaction tricks I have seen.
http://www.emagictricks.co.uk/product_i ... ts_id=3902
Now as for cards - what level are you looking for something really easy/self working or are you up for a few basic sleights?
If you can handles a few basic sleights, then "The colour Monte" is pretty good as it's a whole routine. And, its under 6 quid.
http://www.emagictricks.co.uk/product_i ... ts_id=1122
I know you were asking for self contained card tricks - but if you haven't already got it I would recommend a book as from this you would have hundreds of card tricks literally at your fingertips.
If you haven't already got it I would recommend The Royal Road to Card Magic. (The bible of card magic). and under 9 quid
http://www.emagictricks.co.uk/product_i ... ts_id=4525
Hope this helps