Depending on how well you know the friend, that answer changes. It also depends on how financially well-off you are. The last wedding I attended, I didn't know the couple especially well, so I bought them a $20 set of his and her bath towels. The gift was acceptable. If I knew them a little better, I would have spent a little more. If they were family, I would have spent about $70. It all depends on the situation.