Although I'm eloping, I'll chime in:) I think that guests who chose to attend your DW automatically assume they'll be footing the bill for their travels. After all, it's not like you're asking them to come to your wedding on the North Pole. They are getting some-what of a vacation too.
We were initially planning a DW in Playa del Carmen and had discussed paying for a welcome party, reception, and 1 excursion for our guests. That being said, you certainly don't HAVE to pay for anything for them. I don't think you're required to pay for their meals (other than the reception meal) b/c you wouldn't pay for their meals the days up to and after your wedding if you had it at home.
People have a choice to attend or not, or whether they can afford the trip. You'll have to decide with your FI what you can afford, who (if any) people you will help pay to get there, and then be prepared for some guests you'd like to have there, just flat out not be able to afford the trip.