To be annoyed at having to pay so much for a party organised by SIL?

[Muchadoaboutnuthing]

Dh has 2 sisters, neither of whom we get on with particularly well (LONG back story). FIL is turning 80 in a few weeks. After christmas SILs told us they were thinking of arranging a party for him. We called over to talk to them about it 4 or 5 weeks ago, we wanted to know which weekend it would be on so we could arrange childcare and see if they wanted any help with organising.
At the time the choice was between two venues, I'll call them pub a and pub b. FIL drinks in pub A every Saturday night, has friends that he drinks with in there etc. They said they would reserve an area for us, do free food and have free music. Pub B will charge £5 a head for finger food and we have to provide music. FILs preference was pub A so as far as we were concerned this was sorted.
SIL announced yesterday that they have actually booked pub B and a dj. They have invited over 40 people, many of whom are friends of SILs and their husbands and have no relationship/connection with FIL. They have decided the bill is to be split 3 ways between the 2 of them and DH and I and that we will have to pay between £50 and £100 each, waiting to get confirmed numbers.

AIBU to be a bit annoyed by expecting to pay this amount of money for a party that we had no part in organising, our opinions were never asked, we were led to believe it wouldn't cost us anything as they were having it in the other venue and half of the guest list is made up of their own friends and neighbours? Don't get me wrong, we will pay it, I get on great with FIL and he'll love the party but AIBU to be annoyed?

Can you afford it? If so I'd say suck it up. You have my sympathies.

Can't it be rearranged to pub A or is it too late? I'd challenge the guest list. No way would I pay for something I hadn't agreed in advance.

YABU, it sounds like SIL has basically tried to sucker you into paying for a party for her and her friends. It doesn't sound like she is concerned about FIL enjoyment much at all, or the venue would be pub A with FIL friends and family.

*YABNU, I mean!

YANBU. I would go back and say that I wasn't happy paying out for the opposite choice from that which had been agreed, tbh.

Yes go back and say you don't have the money so can you go with pub A, if not then you can't afford to help but will gladly come and celebrate with him

YANBU. try making your point and asking why not Pub A when thats what you agreed.

Yanbu sounds like its more a party for her and sod what fil wants. I would suggest ts at pub a as that is what fil would like

well if you had it at your house it would cost you a heck of a lot more than £50 or even £100.

I wonder what sort of food Pub A would provide for nothing. And what sort of music.

I might however suggest that if you are feeling brave you could say you will only pay for 1/3 of DJ and the food for FIL's mates, as you have observed that they are inviting a load of their own friends, but good luck with that...

I wouldn't pay. He wanted it at the pub that he considers his local, and this is where is should be held to also include his mates, not random people he never met in a location that isn't regular to him. If she wants a party for her mates, then she can organise and pay for this herself.

My main concern would be that FIL is not having his party in the venue of his choice. I think your DH should dig his heels in and insist you go along with FILs preference. Also, the guest list should be agreed by all of you if you are splitting the payment three ways. If they want to invite some of their own friends they can pay for them. You and DH should draw up a list of FILs friends who are invited plus add on any of his friends who should have been invited and agree, with your SILs that you will each put a certain amount behind the bar at venue A to pay for drinks, but add that you expect them to put a bit more as they are also inviting separate guests unrelated to FILs birthday.
It might sound a bit petty but they sound very cheeky and need to be made aware that you and DH are not doormats.

ps if you're worried about what food Pub A will provide you could ask if it would also be okay to bring along some platters of food as extras 'as you don't want to put them to too much trouble or take advantage'.