Joewr,
What is your itinerary? The way you have it listed is somewhat anti-climatic. Though "I" can have a great time diving in a mud hole, most people tend to be a little disappointed in Yap, and especially Guam, after diving Palau. Not that Yap or Guam is a mud hole compared to Palau, they are just different. Who are you diving with in Yap and Palau, and where are you staying. As far as the boats go here, don't be too put off by the size of the MDA boats (GTDS's boat is about the same size). The diving here is a little different than what you'll find in Yap and Palau. The tour ops are geared toward the Japanese and tend to be cattle operations. MDA and GTDS tend to cater more towards "local" divers. You can do a 2-tank trip for $40. If you're sure you want to do the smaller boats, MDA has their smaller Reef Dreams. A few friends and I have taken this boat out a couple of times to get to some of the more remote locations and it's a nice set up. The thing with the Reef Dreams is that it doesn't go out on a daily schedule so you may have to "charter" it. Depending on what day you are here, I might be able to fill a couple of spots on it to bring your cost down. If your interested in doing some shore diving, I'm almost always getting wet on the weekends, and can almost always be talked into a late afternoon (I get of work at 3:30), or a night dive during the week. Well my wife is after me to get my stuff ready to go diving, so I'll talk at ya later.
Rooster