...a friend from school has invited me to her wedding. It seems they aren't having a reception, just the ceremony and a disco afterwards with a five (!) hour gap in the middle. They take place in two separate rural locations and I know there is nothing to do nearby. I was generally excited about a wedding at the time and I do like celebrating the actual ceremony with friends but it will be an expensive trip to sit in a car for five hours in the middle of nowhere, all dressed up.
Is it rude to reply and accept for the ceremony but not the disco? Or, having received the 'save the date' note months ago is it now okay to say we can't make it? We are not especially close and I know I am (at the least) b-list whilst DP's name was squeezed into the edge of the card after mine had filled the space 
so I doubt we'll be missed. OTOH I don't want to cause offence as we do vaguely keep in contact on facebook.
I received the formal invite a week before the RSVP deadline and my dithering means I have now overshot it by several days so I do need to reply today or tomorrow. I've never turned down a wedding invite, wholly or partially, before (not had that many!) so don't know what to write.