If you're expected to pay for something I think it's okay to politely question the reasoning behind it, especially if you see something that looks very similar but cheaper. Maybe start by asking if there's a particular reason for X, because there are Y and Z options that seem similar but cost less, just curious about why. I think if people are asking others to spend money they should be able to explain why they're going with certain more expensive options. BM1 or 2 or whoever presumably volunteered to be in charge of organizing each activity and they should be doing it responsibly--not necessarily spending hours scouring the Internet for comparable items, but they also shouldn't be picking the first thing that comes to hand. And they should be aware of hidden/indirect fees, like delivery and parking, if they expect others to chip in on those.
I think the awkwardness could come if they don't seem to have a good reason, or they don't have what you think is a good reason. Like maybe someone says, "Well, that cheaper hotel is in a dodgy area, I've been there," and you're thinking, "I've been there too and it's perfectly fine." Personally I probably wouldn't try to change anyone's mind on that point, but I would keep my overall budget in mind and not exceed it. Like, "Okay, Hotel X and Spa Y sound great. But, to be honest, I can't afford to use those, AND go for dinner at Restaurant Z. I'm going to bow out of the dinner, unless you guys want to talk about cheaper alternatives to X and Y." Well, I don't like that wording... It shouldn't ever be like you're trying to force them into getting something cheaper that no one else wants, by withholding your presence from an activity. But on the other hand you shouldn't have to spend more money than you're comfortable with, as long as you give them plenty of notice when you can't commit to something.