I tend toward the group tip basket approach because even if you noticed one guy for something in particular, perhaps you didn't notice the others because they were also doing a good job. For example, no cares about tech support until you need it, then they're fantastic until they fade back again because everything is working.
I also tend toward if you think you can't afford the tip, you can't afford the trip. For the prices we're talking about, it's not going to seriously break anyone. While you might not do $500, a couple hundred ought to be in reach. I'd reckon very VERY few who go on multi-thousand dollar trips literally could not afford to pay it. Someone might not WANT to pay it, but could. I just don't think it necessarily right either to go on a boat where tips are geared as a large part of the compensation and skip that because you either don't want to or can't pay. Perhaps you could just say upfront that you'd like only basic care, so you won't owe...
Heck, we're pretty lucky that they are making a portion of the cost variable. If they included tips, we'd probably end up paying more.