Feridust, I have been thinking long and hard about this. It has occurred to me that the answer actually depends on you and your involvement in the wedding plans.

In what manner are you contributing to the planning and carrying out of this wedding and reception? I mean not just the contribution of time but the contribution of money? Yes, you need to provide a gift. It should then reflect the contribution(s) you have and have not made. If they have basically done all the planning and are footing the bill you need to provide them a gift that recognises this. It would have to be pretty substantial. Me, I would give what money I could afford. On the contrary, if you have been part of the planning process and been contributing towards the cost of the day then you merely need acknowledge the other parents. That very fine bottle of wine will more than suffice if you are thusly on equal footing.