I've had a lot of family do destination weddings and you know who eats the cost of going? The family. Why? Because it's the nice thing to do. Basically, as the people who are holding the wedding the nicest thing to do is to find affordable travel options. Basically, providing guests with a range of options and finding ways to cut the cost. You could even say that you do not ask for gifts if they choose to attend. Basically, it's this:

"Dear family, we realize this is a costly venture so we understand 100% if you are unable to make it. However, if you would like to join us on our special day here are some accommodation options that we have found in different price ranges."

Another option is to have a reception back home. I've had family do that as well for the family that couldn't make it to the wedding that was far away or in a small church. Basically, it is at your own personal discretion how you want to do this. It's YOUR wedding and if you want it small and to not have to foot the cost for your extended family then don't. It's not your job to. If they want to come, the nicest thing to do is to find cost cutting ways for them in advance and then let them decide. If you find that no one is interested? Make the wedding smalll and then have a party when you get back.

I had a friend who got married in the middle of nowhere in iceland with just her, her husband, the priest and a photographer. They had a MASSIVE party upon their return. I also had a cousin who got married in a small church and invited only immediate family and had a large reception about two months later. I also had a family member who got married in florida which is no where near where the rest of my family is, and the wedding was small but the party was amazing and that's where the money went but the extended family ate the cost of going/flying because it's a way of providing support for that family member. They were also pretty well off, but not one person expected them to eat the cost of the entire family, because that's fucking absurd.