How much money is appropriate to spend on a wedding gift?

Do you typically spend a set amount on a wedding present, or does it depend on your relationship with the bride/groom? If you spend a set amount, please ignore the lengthy discussion below :)

In the next month, I will be attending the wedding of two friends of mine. I have known them since elementary school (the bride) and middle school (the groom). Throughout my adolescence, I was extremely close with both; taking most of my classes with the groom and playing in a band as well as school orchestra with the bride. We hung out in the same group throughout most of high school, continuing to hang out together into college when everyone got together for holidays and summer.

Post-college, I am no longer as close with either. Both the groom and I have moved across the country, but we still speak regularly. I communicate with the bride mostly on facebook. They are having a smaller wedding, and seem to have only invited a select group of friends. How much is appropriate to spend on this particular wedding?