i'd say about 5k would be apropriate, as long as you've had a winning week or month betting on games.. if you've been losing i'd say about 1k would be fine
a little closer to the range i expected, i dont think 50 works, you dont want to give less than what they probably spent on you and your date. I would think a few hundred would work as a gift for a good friends wedding
and it should absolutely be cash. If there is anything they want so much that they would value it more than the money, they would have already bought it