It is perfectly acceptable to ask others what they are giving, although you do not have to be guided by that. There was no "guess" as to amounts. The amounts generally considered "normal" were given. Those are statistics though. The amount all depends on the closeness of the wedding party to your family, and the amount that you are comfortable giving.
For a family that makes $50,000 per year and gets 4 wedding invitations for the month of August, they cannot afford to give each couple a gift of $200 and up, regardless of how much they love them. If someone makes $1,000,000 per year and wants to write a check for $10,000-20,000 that is also fine.
If there were a cut-and-dried "admission price" for a wedding, I would have given it to you. There isn't. What most people give was stated based on statistics, but if that strains your budget, you should give what you can afford along with your best wishes.
I'm sorry if that isn't what you want to hear, but it is the truth.