All of this preferably should be decided between the future machetonim BEFORE the engagement, in fact it might not be a bad idea if the shadchan can find out what each side is thinking along these lines, before the shidduch goes through.
We did 50-50 in both our weddings – one son and one daughter – at the machetonims’ suggestions, and so far it seems that the idea is accepted as such as the FLOP(S) idea. When we cheshboned it out, it came to approximately the same expenses whether we had split the costs or done FLOPS.
it used to be that the girl’s side paid exclusively for the hall, but that is no longer the only option.