thistlechaser | Northern Cal, socially clueful folk? :)

Since I have the social skills of a large rock, I'm looking for a bit of advice:

A co worker is getting married. While he's not a member of our work-group, he's as close as you can get to it without being one. I work with him on a weekly basis, and our desks are next to each other. I like him (as a co worker and a person, but we don't go and hang out after work or do anything outside the job).

He's getting married. While I'm not invited to the wedding, I'm invited to a ... I guess dinner? To some sort of wedding-related social thing for friends and co workers not invited to the wedding.

While I like the guy, I'm not going. I'm assuming since I was invited that I should send a "gift" (check). My question is, how much would be a good gift? Because I like him and work with him on a regular basis, I do *not* want to look cheap. I was thinking $50? Anyone have an opinion on that sounding high, low, or okay? (I specify northern California because everything's more expensive here, so I'm assuming gifts would be larger as well.)