If your friend is on a very tight budget, then I don't think it is unreasonable to ask the grooms men to pay for their rentals. The same with the bridesmaids paying for their dresses. Not everyone is willing to spend silly amounts of money on their weddings.
If the grooms men and bridesmaids do have to pay for their clobber for the day, then they should have more of a say in the style and cost.
I like to tell people I have the heart of a small boy. Then I say it's in a jar on my desk.