Open Bar vs. Consumption Bar? Help!

Hi friends. I have been going back and forth with my parents recently on the bar packages for our venue. When we first started planning months ago, we had originally agreed on a 5 hour, limited spirits open bar package. This includes beer, wine, regular shelf liquor options & mixers, and a champagne toast for the bridal party. I’m now working on getting the details and deposit finalized. I sent the contract over to them to review last night, they agreed it looked good, and sent me the deposit.


Maybe an hour later my stepmom texted me asking why there isn’t a champagne toast for all guests (we didn’t feel it was necessary/just another expense) and is being super analytical of how many drinks each guest might drink, suggested maybe we should bring the guest count down (tried to discuss that with my fiancé and that caused an argument as the number of people on our guest list hasn’t been an issue till now), or maybe do a consumption bar instead. I’m now doing research on if it’s better/more cost effective to have an open bar versus a consumption bar. I am eternally grateful to have the help of my parents for our wedding because I know many couples have different situations. But changing what we previously agreed on, asking to bring the count down, or adding things we didn’t originally want is just feeling a little bit overwhelming to me. They’re telling me not to worry about cost, but I totally am.
For reference, we have a pretty close group of friends who like to drink/party/have fun. I’m in no way advocating for everyone to get hammered, but I worry about doing the consumption bar and it being a way bigger bill than my parents anticipate on having and I don’t want them or us to be caught with any surprise bills.
If anybody has any advice or experiences with open bar versus consumption bar, I would be very grateful! Thank you.