I live on Guam and will be happy to answer any questions you have! If you have a plane ticket and a free place to stay, you've knocked out the most expensive part. Eating out is comparable in price to the US mainland, and there are vegan options (specifically veg places are: Healthy Hearts, Cafe Dharma, and Simply Food are veggie lunch shops, Fortune Cookie Cafe and Palm Cafe have vegan menus, Hava Java and Infusions have soy coffees, but Infusions also has vegan muffins so they win). Groceries are more expensive than the mainland if your friends do not have base access, but they're not hideously expensive. Do you dive? If you are interested in getting dive certified it is super cheap here. You could have a super awesome dive vacation by using Guam as your hopping-off point to visit Palau and/or Yap, Truk, etc. Check out the travel page on
www.mdaguam.com . I would need to know a little more about what you're interested in doing, if you want to just chill on the beach, go out at night, etc etc.... but I can help :)