If that's not right, it's certainly very, very close! Some of the images looks just like it, some slightly less so (probably just a variable species).
Thanks!
As you may have noticed, I've been working through some of these bugs trying to get IDs - you may just have saved me some work when I get to Monteverde's ones!
Just checked out the very useful website below, and I am now pretty certain it is Dorphia horcana - the only two other species of the genus listed in Costa Rica are D. nora and D. avia, neither of which look anything like the moth pictured above.